Are you incapable of making your argument without this?
Are you in this just to make people squirm?
If you are all for it, then be all for it. Don't assume other things will happen.
Churches are private institutions, as long as they do not accept federal funds they do not have to marry gay and lesbian couples. That is the law and that will stand in court. There is a mountain of prescedent for it. Gays and lesbians will be welcome in the majority of american churches, the fringes and the baptists can do whatever the hell they want. Once gay marriage becomes lawful and it starts happening widespread public perceptions will sway heavily in favor, pressure will be placed from the inside and the major, non-radical sects of christianity will bow or face a mass exodous to a tolerant religion that will.
This will all change on the "free market" No need for government regulations.
I don't think gays want to be baptist anyway.