Are you sure? Because they've changed their mind on other issues that were once accepted by the mainstream before they turned reprehensible. The LDS church won't allow itself to be seen as a fringe organization. They will conform with the mainstream.
I think so. I think they want to be seen as firm in their morals and convictions. Even if they did they would not pretend that they supported it all along.
You see it as them becoming fringe and they will see it as standing for what they see as right. Keep in mind that gay marriage is largely a US fight and the Mormon church is global.