Perhaps that's because their anti-Christian bias doesn't come from a rational place (to state the obvious).
It's entirely emotional, so they can't see the anti-Conservatism that comes with their bigotry.
I can see that - But it is antithetical, and in direct opposition to Conservative thought - As much as is possible, federalism is designed to let folks be, and let them govern themselves (as a people, a county or town, and as a state), as they see fit.
And in the offing, it provides at least 50, and more likely thousands of little petri dishes where folks can try things out and adopt that which works best for them. That is what the federal edict removes.
If in fact the naysayers are right, then there is nothing to stop them from moving, banding together, and try their own experiment to prove their case and their cause...
I would not stop them, and see it as their right... But they would stop me, and every other person, by issuing from on high. That is not Conservatism.