I registered solely to say this.
You're just being too accomadating is all. Trying to get everyone to "get along" as if that were at all possible.
Pick a side and stick to it. Enforce that side with an iron fist and ban everyone else. Sure, they'll bitch about it. So what? They can go find another website if they're so unhappy. Fuck em. It's YOUR site. Nobody is forcing them to come here. If they're unhappy, they can leave.
It's all there, in black and white:
Democratic Underground is an online community for Democrats and other progressives. Members are expected to be generally supportive of progressive ideals, and to support Democratic candidates for political office.
That's your side. Period, end of story.
If people don't want to support the
Democrat, they can go to any of the other zillion message boards out there to bitch. It's one thing to say "I don't like the way Obama is doing this or that but I'll vote for him" and quite another to say "I'm not supporting Obama at all unless he does this or that and the other!".
Ban the latter.