Because they're the closest thing to the NRA that we have. They are, in my opinion, the only nationwide group that has any chance of defeating the inevitable NRA pushback. Even the most sensible gun laws, laws that might even have a chance at passing, will be fought tooth and nail by these murder-profiteering bastards, and every DUer knows it.
I joined the day after the Aurora massacre, and I hope that if anything good can possibly come out of Newton, it will be the prevention of any more violence like we saw on Friday. No more dead children, no more dead teachers. And no more bullshit gun industry lobbies.