Now, it’s important for me to make clear what I am not saying. I am not saying that today’s progressives are “the real racists.” I am not saying that same-sex marriage or any other progressive social movement is the equivalent of racism. Today’s progressives have at best a fuzzy lineage with yesteryear’s, and all of us are implicated in this civilizational enormity; as one who is “conservative” by today’s political standards but firmly in the camp of Enlightenment liberalism, i.e. a “progressive” on the scale of millennia, I don’t exculpate myself from this legacy. Not all racists were progressives and not all progressives were racists (it was the French Revolutionaries who banned slavery in the French colonies, for example). No group, ideological, religious or otherwise comes out of that complex history looking good (which itself should warn us off easy narratives of Progress versus the Dark Ages).

What I am saying, however, is that the conventional wisdom on social change is wrong. The conventional wisdom sees our civilization’s still-incomplete turn away from racism over the past 50 years as the cornerstone case for the inevitability, goodness, and irreversibility of socio-cultural revolution. In fact, it was not a “socio-cultural revolution,” it was the halting and reversing of a socio-cultural revolution.

Can we draw any lessons from this? Well, that’s risky business. But one potential lesson is that while socio-cultural revolutions are reversible, they take a long time to play out — 150 years in this case.