Background of the Issue "Should Gay Marriage Be Legal?"
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Same-sex marriage supporters protest the passage of Proposition 8 in front of San Francisco City Hall. Source: Darryl Bush, www.ap.org, Nov. 15, 2008
On June 26, 2015, the US Supreme Court ruled that gay marriage is a right protected by the US Constitution in all 50 states. Prior to their decision, same-sex marriage was already legal in 37 states and Washington DC, but was banned in the remaining 13. US public opinion had shifted significantly over the years, from 27% approval of gay marriage in 1996 to 60% in 2015.
Proponents of legal gay marriage contend that gay marriage bans are discriminatory and unconstitutional, and that same-sex couples should have access to all the benefits enjoyed by different-sex couples.
Opponents contend that marriage has traditionally been defined as being between one man and one woman, and that marriage is primarily for procreation.
Gay Rights, 1960-1980s
The gay rights movement in the US can be traced back to the Stonewall Riots that occurred following a police raid on the Stonewall Inn in New York City at 3 a.m. on June 28, 1969. Police raids on gay bars were commonplace, but on this occasion the gay and lesbian patrons fought back and sparked days of protests. The Stonewall Riots marked the beginning of a political movement for gay rights during a time when it was illegal to have homosexual sex in all states except for Illinois.  Between 1969 and 1974, the number of gay organizations in the country swelled from fewer than 50 to nearly a thousand. 
Gay-rights activism in the 1970s focused more on personal liberation and visibility than on gaining access to institutions such as marriage. While some gay activists sought the right to marry in the early 1970s, others rejected marriage as "heterosexist” and saw it as an outdated institution.  The gay liberation movement achieved a victory in Dec. 1973 when the American Psychiatric Association declassified homosexuality as a mental disorder and the American Psychological Association did the same in 1975. 
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Timeline of Same-Sex Marriage Bans and Legalizations by Effective Date of Laws Source: "33 States with Legal Gay Marriage and 17 States with Same-Sex Marriage Bans," ProCon.org, Nov. 13, 2014
The increased visibility of the gay community prompted a well publicized backlash by opponents of gay-rights. One high-profile opponent of gay rights was singer and former Miss Oklahoma Anita Bryant who founded the group Save Our Children and campaigned to repeal local ordinances that prohibited discrimination based on sexual orientation. During the 1980s, news of the AIDS epidemic increased homophobia and discrimination but also encouraged the gay community to further organize. Following the news that actor Rock Hudson was dying of AIDS, attitudes towards both AIDS and the gay community started to shift. In 1983, Congressman Gerry Studds (D-MA) became the first openly gay Congressman, followed by Congressman Barney Frank (D-MA) in 1987. 
Gay Marriage Debate, 1990-2010
The current national debate on gay marriage was sparked by the Supreme Court of Hawaii’s 3-1 ruling on May 5, 1993 that the state could not ban same-sex marriages without "a compelling reason” to do so.  The case was sent back to a lower court but voters approved a constitutional amendment to ban same-sex marriage before the courts settled the issue. Although a gay marriage was never performed in Hawaii, the issue gained national attention and prompted over 40 states over the next decade to pass Defense of Marriage Acts (DOMAs) that defined marriage as a legal union between one man and one woman.  On Sep. 21, 1996, President Bill Clinton signed the federal Defense of Marriage Act into law which defined marriage at the federal level as between a man and a woman. The federal DOMA statute ensured that no state would be forced to recognize gay marriages performed in other states and prevented same-sex couples from receiving federal protections and benefits given to married heterosexual couples.
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US gay marriage laws, state by state Source: Ned Flaherty, "State-Level Marriage Equality,” www.marriagequality.org, Feb. 16, 2012
On Dec. 20, 1999, the Vermont Supreme Court ruled unanimously in Baker v. Vermont that same-sex couples were entitled to the same rights, protections, and benefits as heterosexual couples.  On July 1, 2000, Vermont became the first state in the US to institute civil unions, giving same-sex couples the same rights as heterosexual married couples without calling it marriage.
On June 26, 2003, the US Supreme Court ruled 6-3 in Lawrence v. Texas that sodomy laws were unconstitutional. In overruling the court’s June 30, 1986 decision in Bowers v. Hardwick, the court established a right to sexual privacy and Justice Antonin Scalia predicted in his dissent that the majority decision "leaves on pretty shaky grounds state laws limiting marriage to opposite-sex couples.”
On Nov. 18, 2003, Massachusetts highest court ruled that the state must allow same-sex couples to marry. Unlike the 1999 Vermont Supreme Court ruling, the Massachusetts Supreme Judicial Court did not provide the legislature the opportunity to offer an alternative to marriage such as civil unions. On May 17, 2004, the first legal gay marriage in the US was performed in Cambridge, MA between Tanya McCloskey, a massage therapist, and Marcia Kadish, an employment manager at an engineering firm. 
Before 2004, four states had banned gay marriages. In 2004, 13 states saw their constitutions amended by referenda to ban gay marriage. Between 2005 and Sep. 15, 2010, 14 more states followed suit, bringing the total number of states with constitutional bans on gay marriage to 30. 
On July 14, 2004, an effort in the US Senate to pass a constitutional amendment to ban gay marriage received only 48 votes of the necessary 60 votes for the proposal to proceed. On Sep. 30, 2004, the US House of Representatives also rejected a constitutional amendment to ban gay marriage by a vote of 227 to 186, 49 votes shy of the necessary two-thirds majority. 
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Out-of-wedlock births in the Netherlands, 1970-2003 Source: Stanley Kurtz, PhD, "Going Dutch?” www.weeklystandard.com, May 31, 2004
California, with the nation’s largest and most racially diverse gay and lesbian population, has played a prominent role in the modern gay marriage debate. On Feb. 15, 2004, San Francisco Mayor Gavin Newsom ordered the city to begin issuing marriage licenses to same sex-couples. On Mar. 11, 2004 the California Supreme Court ordered a halt to same-sex weddings and voided the marriages on Aug. 12, 2004. In a 4-3 ruling on May 15, 2008, the California Supreme Court overturned state laws banning gay marriage.  Between May 2008 and Nov. 4, 2008, an estimated 18,000 same-sex couples married in CA.  On Nov. 4, 2008, 52.3% of California voters approved ballot measure Proposition 8 which made same-sex marriage illegal in the state. On May 26, 2009, the California Supreme Court upheld Proposition 8’s gay marriage ban, but on Aug. 4, 2010, US District Judge Vaughn R. Walker struck down Proposition 8 as unconstitutional , and on Feb. 7, 2012, a three-judge panel of the US 9th Circuit Court of Appeals upheld Walker’s ruling.  Following Judge Walker's ruling, many organizations expressed their views on gay marriage.
On Aug. 4, 2010, the Church of Jesus Christ of Latter-Day Saints released a statement saying, "Marriage between a man and a woman is the bedrock of society."  On Aug. 10, 2010, the American Bar Association's House of Delegates voted to support gay marriage.  The following day, the American Psychological Association reiterated its support for same-sex marriage.  In a Sep. 13, 2010 speech, Pope Benedict XVI expressed his opposition to gay marriage, saying the Roman Catholic Church "cannot approve of legal initiatives that imply a re-evaluation of the life of the couple and the family." 
From 1988 to 2010, public support for gay marriage increased at a rate of 1 to 1.5 points per year.  On Aug. 11, 2010, CNN released the results of the first national poll to show a majority support for gay marriage, with 52% agreeing that "gays and lesbians should have a constitutional right to get married and have their marriage recognized by law as valid.”  A Gallup report released on May 8, 2012 found that national support for same-sex marriage peaked in 2011 at 53%, dropping to 50% in 2012. 
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US gay marriage polls, 1996-2015 Source: Justin McCarthy, "Record-High 60% of Americans Support Same-Sex Marriage," gallup.com, May 19, 2015
Repeal of DOMA: US Supreme Court Enters the Debate
On July 19, 2011, the Obama administration announced that it would support a bill by Sen. Dianne Feinstein (D-CA) to repeal the Defense of Marriage Act (DOMA). This followed President Obama's decision on Feb. 23, 2011 to instruct the Justice Department to stop defending DOMA, the federal law that defines marriage as a legal union between a man and woman, over concerns that it violates the equal protection component of the Fifth Amendment. 
On May 9, 2012, President Obama became the first sitting US president to declare his support for gay marriage, stating: "At a certain point, I've just concluded that for me personally it is important for me to go ahead and affirm that I think same-sex couples should be able to get married." 
On June 26, 2013, the US Supreme Court in a 5-4 decision in United States v. Windsor declared unconstitutional part of the federal Defense of Marriage Act (DOMA) which defined marriage solely as a legal union between a man and a woman. The decision allowed same-sex married couples to receive the same federal benefits granted to heterosexual married couples, including tax breaks and pension rights. 
Also on June 26, 2013, and also in a 5-4 decision, the US Supreme Court ruled in Hollingsworth v. Perry that proponents of California’s Proposition 8 lacked "standing" to defend the anti-gay marriage measure after it had been ruled unconstitutional by a District Court. The decision was considered to clear the way for gay marriage to become legal again in the state. 
In 2013 and 2014, following the US Supreme Court's United States v. Windsor decision, gay marriage bans were overturned by court rulings in several states, but those rulings were put on hold pending appeals to the US Supreme Court. On Oct. 6, 2014, the Supreme Court declined to hear appeals from five of those states, and the decision immediately cleared the way for legal gay marriage in Indiana, Oklahoma, Utah, Virginia, and Wisconsin. Six other states in which gay marriage bans had been overturned, Colorado, Kansas, North Carolina, South Carolina, West Virginia, and Wyoming, were also affected by the Supreme Court ruling because they were in the jurisdictions of the lower courts that had overturned the gay marriage bans. 
Gay Marriage Legalized by US Supreme Court (and Related Backlash)
On Apr. 28, 2015, the US Supreme Court heard oral arguments in Obergefell v. Hodges about whether or not gay marriage is a right guaranteed by the US Constitution, and whether or not gay marriages performed in states where it has been legalized must be recognized in states that ban the practice.  On June 26, 2015, the US Supreme Court ruled 5-4 that the US Constitution guarantees the right for same-sex couples to marry in all 50 US states. Associate Justice Anthony Kennedy stated in the majority opinion: "The Court, in this decision, holds same-sex couples may exercise the fundamental right to marry in all States." 
After the Supreme Court ruling, there was some backlash in states where their bans had been overturned by the Obergefell v. Hodges ruling. Several county clerks resigned or refused to issue marriage licenses to gay couples (or to grant marriage licenses to anyone), citing government infringement on their personal religious beliefs.  Most publicly, County Clerk Kim Davis in Rowan County, Kentucky, was briefly jailed in Sep. 2015 for contempt of court when she refused to issue marriage licenses to gay couples and ordered her employees to do the same. Davis was released from jail when her employees began issuing licenses in her absence and said they would continue to do so upon her return to work. 
On Jan. 6, 2016, Alabama Chief Justice Roy Moore ordered state probate judges to not issue marriage licenses to same-sex couples. He had issued a similar ruling in Feb. 2015 after a federal court struck down Alabama's ban on gay marriage. It remains unclear whether state probate judges are following these orders. 
Same-Sex Marriage in the World Today
As of June 26, 2015, 19 out of 194 countries allow same-sex couples to marry nationwide. The world's first legal gay marriage ceremony took place in the Netherlands on Apr. 1, 2001, just after midnight. The four couples, one female and three male, were married in a televised ceremony officiated by the mayor of Amsterdam.  In addition to the Netherlands, gay marriage is legal nationwide in Belgium (2003), Spain (2005), Canada (2005), South Africa (2006), Norway (2009), Sweden (2009), Argentina (2010), Iceland (2010), Portugal (2010), Denmark (2012), Uruguay (2013), New Zealand (2013), Brazil (2013), France (2013), Luxembourg (2014), Finland (2014), Ireland (2015), and the United States (2015). Same-sex marriage is legal in some jurisdictions of Mexico and the United Kingdom (England, Scotland, and Wales, but not Northern Ireland).