In Alabama, a same-sex marriage fight is upon us. Last month, a federal judge struck down the state's law against the unions. But Sunday night, "in a dramatic show of defiance toward the federal judiciary, Chief Justice Roy S. Moore of the Alabama Supreme Court ordered the state’s probate judges not to issue marriage licenses to gay couples on Monday, the day same-sex marriages were expected to begin."

It's unclear how the state's 68 probate judges will react. For the Alabama couples planning to marry today, the order could prove meaningless or another obstacle to equality.

Same-sex couples are free to marry one another in 36 states and Washington, D.C. Elsewhere, legal challenges are in motion, and generational changes in attitudes toward homosexuality predict future victories at the ballot box as well. Already, changing laws have allowed more than 70,000 couples to join as one on wedding days that many will recall as the happiest or most meaningful of their lives.

But there are still millions who insist same-sex couples should be denied a place in this social institution, some out of sincere religious conviction, others out of anti-gay bigotry. Religious objections to same-sex marriage are likely to endure for generations, but the anti-gay marriage coalition isn't big enough to win once bigotry fades.

Why fight to delay the inevitable when gays in places like Alabama suffer as a result?

The controversy in Alabama will be seen as an instance of a southern state battling the federal government to deny equal rights to a minority group. "Chief Justice Moore rose to national prominence in the early 2000s when he defied a federal judge’s order to remove a Ten Commandments monument from a Montgomery building and was subsequently ousted from his post leading the high court," The New York Times reports. "He staged a comeback, became chief justice again in 2013, and has ... said that Alabama’s probate judges are not bound by a federal trial court ... His argument has deep resonance in a place where a governor, George Wallace, stood in a doorway of the University of Alabama in 1963 in an unsuccessful bid to block its federally ordered integration."

Debates on this subject usually turn on whether or to what degree the comparison between segregationists and opponents of gay marriage is accurate or fair. Less noticed is the most significant difference between the two civil rights battles.

States' rights delayed the equality of blacks.

In contrast, federalism has hastened the advance of gay marriage. According to Pew, the first time more Americans supported than opposed gay marriage was in 2011. And it didn't reach 50 percent support until 2013—the same year that a key provision of the Defense of Marriage Act was ruled unconstitutional (an outcome owed partly to states' rights arguments). And it's hard to imagine gay marriage getting through a post-2013 Congress with even one chamber controlled by Republicans.

Whereas a state-by-state approach, proceeding via the ballot box, legislatures, and challenges referencing state constitutions, brought gay marriage to Massachusetts in 2003; Connecticut in 2008; Iowa and Vermont in 2009; New Hampshire in 2010; New York in 2011; Maine and Washington in 2012; California, Delaware, Hawaii, Maryland, Minnesota, New Jersey, New Mexico, and Rhode Island and Providence Plantations in 2013; and 19 more states after that.

The earliest states to legalize gay marriage almost certainly helped to shift public opinion at the national level: The nation saw touching photographs from weddings; activists newly convinced in the possibility of victory joined the cause; and everybody saw that no apparent catastrophe ensued after same-sex couples wed. More states started grappling with the fact that their residents could go elsewhere to marry even if they weren't yet allowed to do so in their hometowns. And for some, refusing to recognize the union of people who'd wed elsewhere was too much.

That's what changed their mind.

Legality in just a few states also enabled TV shows and films to portray gay weddings as normal celebrations rather than unrealistic fantasy or politicized protest. And again, tens of thousands of people were actually able to marry one another long before there was any chance of a national gay marriage bill in a country where Barack Obama didn't even voice support for the practice until 2012.

Obama has continued to "evolve," and now claims that the U.S. Constitution guarantees gays the right to marry. The Supreme Court intends to rule on that matter by June, and if it declares same-sex marriage the law of the land, it will obviously hasten the advent of marriage equality in a lot of states. Without addressing the merits of the Constitutional argument, I'd guess that without the early adopting states that helped this movement gain momentum, the high court would be far less likely to be considering this case now and less likely to rule for gay equality.

If the Supreme Court rules that there is no federal right to same-sex marriage, the fight for equality will take longer and justice will be delayed for a lot of gay couples. There will, however, only be two states—Mississippi and Louisiana—where a couple can't drive across the border to a neighboring state where gay marriage is legal, and the only real uncertainty is which state will embrace justice last.

As for Alabama and any probate judges who do start issuing marriage licenses today, Quin Hillyer asks, "What happens to the newly recognized same-sex arrangements if, five months from now, the Supreme Court correctly decides that the Constitution is silent on same-sex marriages, and thus that the decision to recognize them (or not to do so) remains squarely within each state’s sovereign authority?" What happens (without addressing the merits of the Constitutional argument) is that Alabama officials either let same-sex marriages stand or they look like callous jerks for trying to strip husbands and wives of their spouses. No one ever won the American people over by tearing up marriage certificates.