Gallagher on Culture: part V

Part 5, at The Corner, NRO.

Here's another way that gay marriage and no-fault divorce are similar: Elites coalesced in favor of this legal change — and firmly downplayed the very idea it could have any cultural effects at all. Unilateral-divorce laws were passed by insider experts, "the best and brightest," who firmly swore that the objections and reservations of religious people and of the masses were uninformed, ignorant, and unlikely.

Because, after all, how could letting Anna and Evan disrupt their horrible, violent marriage more easily possibly affect your marriage?

Being Americans, even the smartest among us find institutional effects easy to deny and hard to take into account.
....
The heart of the same-sex marriage argument, by contrast, is this: There is no rational, relevant difference between same-sex and opposite-sex couples — and anyone who disagrees is engaging in illegitimate discrimination, similar to people who opposed interracial marriage.

I know gay-marriage advocates honestly believe this to be true. That's not in question. My question is: How can an intellectual both say this and also say that same-sex marriage is not going to affect anyone besides gay couples? (e.g.: How exactly do we treat people and institutions that oppose interracial marriage these days? In law? In culture?)