In some societies, the move toward gay marriage rights is like a high-speed train. Once it gets rolling, it is relentless and unidirectional.
In others, it is the little engine that could.
The ruling by a federal judge in California to strike down the state's ban on same-sex marriage does not take the fight for marriage equality in the United States over the top. But it takes it farther up the mountain than any legal decision before it and propels the issue toward the final arbiters at the U.S. Supreme Court.
On Wednesday, District Court Judge Vaughn Walker, whose own homosexuality was described as an "open secret" by the San Francisco Chronicle, struck down Proposition 8. The controversial 2008 California ballot initiative, which passed with 52 per cent of the popular vote, amended the state Constitution to ban gay marriage. Its passage came only five months, and the issuance of 18,000 same-sex marriage licences, after the California Supreme Court allowed gays to tie the knot.
Judge Walker ruled that Proposition 8 "both unconstitutionally burdens the exercise of a fundamental right to marry and creates an irrational classification on the basis of sexual orientation."
This marks the first time an American court has established that gays and lesbians have a right to marry under the U.S. Constitution's equal-protection clause. Previous legal victories - in Massachusetts, Connecticut and Iowa - applied only to state laws and constitutions. They did not extend gay rights beyond state borders. Judge Walker's ruling, if upheld by the Supreme Court, would apply nationally.
"This just in: Equality won!" Ellen DeGeneres tweeted only moments after Judge Walker issued the opinion in his San Francisco courtroom. Even Paris Hilton weighed in, calling it "a huge historical day for equal rights" and opining "there shouldn't be a law on true love."
Their enthusiasm may not last. The current composition of the Supreme Court, empirically proven to be the most conservative since the 1930s, means the case is hardly a slam dunk for the equal-rights camp.
"This is a high-risk case and many people in the gay-rights community are opposed to this lawsuit," UCLA law professor Adam Winkler explained in an interview. "The risk is especially great because a strong Supreme Court ruling denying gay marriage would push back the possibility of gaining recognition of same-sex marriage by years, if not decades."
Still, many gay-marriage advocates think the risk is worth taking. The current situation amounts to a crazy quilt of rights, in which the legal status of gay marriage changes at the state line. Five states and the District of Columbia allow same-sex marriage, either because their courts forced them to or their legislators voted to do so.
California and Maine granted gays the legal right to marry only to take it away a few months later. Three states recognize gay couples married elsewhere but don't allow gays to tie the knot within their own borders. Thirty states have outright constitutional bans on same-sex marriage.
Then there is the federal Defence of Marriage Act, which deprives same-sex couples - even those who are legally married under state law - of federal benefits such as Social Security.
The only ways to equalize rights across the country would be if Congress itself legalized gay marriage (not likely, given the unbending opposition of senators from conservative states and President Barack Obama himself) or through a Supreme Court ruling.
Prof. Winkler noted that two landmark gay-rights rulings handed down in recent years by the Supreme Court, including one that invalidated Texas's anti-sodomy law, were both written by Justice Anthony Kennedy. Though he sides most often with the conservative clique led by Chief Justice John Roberts, Justice Kennedy is considered the "swing vote" on the nine-member court and could tip the balance in favour of gay marriage.
"That is what the lawyers who brought this case are counting on," Prof. Winkler added, referring to Theodore Olson and David Boies.
The duo last made history when they argued against each other in Bush v. Gore, the Supreme Court ruling that decided the 2000 election. And the teaming up of a prominent conservative lawyer (Mr. Olson) with a noted liberal (Mr. Boies) to fight for gay marriage has made the case a cause célèbre for more than the legal stakes involved.
In explaining his decision to argue the case, and face ostracism in conservative legal circles, Mr. Olson wrote: "This is not a conservative or liberal issue; it is an American one, and it is time that we, as Americans, embraced it."