I think they have already done a good job of attacking the members themselves.
They tell them what to wear, what to drink, what to eat, what to spend their time on, they tell them what to do in the bedroom.
Mormon see wickedness everywhere, because they perceive normal people as evil.
I think they can survive without gays. I think you'll see in 20 years or so the proclamation to the family will be laying next to the journal of discourse.
I think the church could get by just fine were there not gays in the world.
The church operates not by clearly defining the outgroups, but by clearly defining the boundaries. The boundaries may shift and change -- in the past, it encompassed "gentiles," blacks, unwed parents, gays, and lots of others.
The church doesn't need a group of people to demonize so much as it needs a way to set its members apart. In the early 1900's, the church jumped onto the temperance bandwagon and made the WoW mandatory. More recently, the emphasis has been on modesty.