Unless something dramatic changes in the drift of public opinion, the future of religious liberty on these issues is going to depend in part on the magnanimity of gay marriage supporters - the extent to which they are content with political, legal and cultural victories that leave the traditional view of marriage as a minority perspective with some modest purchase in civil society, versus the extent to which they decide to use every possible lever to make traditionalism as radioactive in the America of 2025 as white supremacism or anti-Semitism are today.
So because more and more people might see the anti-gay marriage view for being the bigoted bullshit it is, religious liberty on the issue will be destroyed. For Douthat, religious liberty isn't about being able to think what you want to think. It's about having a lot of people agree with what you think and not be demonized for having a bigoted belief so that you can try to get the gov't to enact that belief into law, at which point everyone who doesn't share your religious belief will have sacrificed their religious liberty so that yours can flourish.
In short, Ross Douthat doesn't understand the concept of religious liberty, nor the concept of the 1st amendment and the basic framework of how our gov't and legal system operate. For him and his fellow conservatives, freedom only matters when it benefits them and them alone. Otherwise liberty is being destroyed. And they wonder why young people who aren't brainwashed by their parents and non-white men aren't voting Republican.
And quickly, I have to disagree with Pierce when he says, "(The government can't make a church do anything.)". Well, it can in the sense that if a church decided it believes in virgin sacrifices the gov't could prevent it from partaking in that practice. As long as a church isn't doing stuff like that, the gov't shouldn't make a church do anything. Nor should a gov't do something just because a church wants it to, which is the concept that escapes many like Douthat on the right.
Update: I was think about this a bit more (because this is where my mind wanders sometimes) and I noticed something odd about the quoted part above. Douthat is complaining that the "traditional" view of marriage will become the minority perspective if us liberals keep pushing it the way we are. But that assumes this whole marriage issue is a zero sum game for us. It's not. We are simply pushing for gay marriage to go along with what they call "traditional" marriage. We don't want to get rid of anything.
Therein lies the implicit bigotry in Douthat's view of traditionalism. Traditionalism for the sake of traditionalism wouldn't be a problem on this issue if gay people weren't excluded. If they hadn't been, us liberals would be arguing in part for keeping a good tradition alive. Douthat only argues for traditionalism because it's what matched his beliefs. If it didn't, he wouldn't be concerned about it.
And of course, his traditionalism has an arbitrary time limit. He hints at it above, I think, when he says, "civil society". I think that's a very vague acknowledgement that there are forms of "traditional" marriage in societies Douthat doesn't consider civil that he doesn't agree with, probably forms like polygamy and arranged marriages. So what these arguments about tradition are really about are just hiding bigoted religious beliefs.