It is an awesome thing to behold when social advances gather such momentum that they move inexorably, unstoppably forward. Then, opponents can only watch as the walls crumble and truths that touch the core of humanity are laid bare.

That happened when black Americans demanded the right to be served at lunch counters and to ride in the front of buses. It happened in East Germany, when the Berlin Wall fell. It happened in South Africa when Nelson Mandela was freed from prison. And it’s happening now as the legal barriers that kept same-sex couples from marrying fall left and right.

In this month, alone, Attorney General Eric Holder announced that the Justice Department is preparing to ensure that married gay and lesbian couples will have the same rights in federal legal matters as heterosexual couples. That will apply even in states where same-sex marriage is not yet legal.

In the federal courts, meanwhile, same-sex marriage is on a roll in some of the nation’s most conservative states. Last Thursday, a federal judge struck down Virginia’s ban on same-sex marriage. In recent weeks, federal courts have rejected similar bans in Oklahoma and Utah. Federal courts have also ruled for same-sex rights in Kentucky and Ohio, while state courts have taken up the cause in New Jersey and New Mexico. Nevada has simply declined to defend its gay marriage ban in court.

Why? Because like apartheid and Jim Crow, these laws were an artifice: rotten structures that cannot withstand the test of time. Laws meant to demean whole classes of human beings by denying them the rights that the majority are permitted to enjoy always come with an expiration date.

Supporters of these bans, some acting on their honest religious beliefs, failed to understand two critical flaws in their thinking. First is that once gays and lesbians stopped closeting themselves, and Americans saw they had close friends and relatives who were harmed by these laws, the end of discrimination was foreordained.

The second is that same-sex marriage is a civil matter, not a religious one. Some people get married in city hall, some in church. No law can require churches to perform same-sex marriages, so religious objections are not germane. The only question is whether governments can prohibit gays and lesbians from having the same marital rights provided to straight couples.

This is now a locomotive and nothing will stop it. It will cause disruption among those who have not shed their fear and disapproval of gays, but things have changed, in the country and in the courts. It’s a welcome moment.