Because a lot of states would move to outlaw the RCC in particular, and orthodox Christianity in general. I think the showdown is going to happen sooner or later in any case.
Better sooner rather than later. With each passing generation, committed Catholics (and Christians in general) in the West are getting fewer and fewer in number. The time to strike at this sort of iniquity is now, while we still have at least some chance to prevail in the hearts and minds of the people at large, and while we are still of sufficient numbers to defend ourselves against genocidal backlashes against the proclamation of the Truth.
While he is still taking furtive steps, Benedict *is* starting the process of reining-in chaotic dissent against the teachings of the Church within her own ranks, both on life issues and other matters. With the prayers and encouragement of the faithful, he will become ever more committed to righting the Barque and returning it to its proper heading. So will his successor. You can *feel* that the Restoration is underway!
I don't think even the Democrats would be stupid enough to do something that unconstitutional.