As deplorable as the crap these people pull is, I think they make a larger negative impact by serving as a scapegoat. They are so extreme with their hatred that they allow the "regular" homophobe to feel better about himself (or herself I guess) and not feel bad for his own actions. The person who doesn't necessarily hate gay people, but sure doesn't want to work closely with one, or see two guys holding hands, the guy who casually uses the "f" word and refers to things he doesn't like as "gay"...he can say, "I'm not a homophobe, those guys are homophobic." And go about his day secure in the knowledge that his feelings towards gay people aren't that bad because there are more extreme people out there.
It's comparable to how an organization like the KKK would allow somebody who maybe isn't openly and aggressively racist to feel better about themselves. I sure we all know somebody like that: They don't have a problem with black people, per se, they just don't want their daughter bringing one home, they probably cross the street or hold their purse a little tighter if they see a group of black teenagers approaching, etc. Having groups of such extremes, groups that are absolutely hate-filled and proud of it, makes others like like they are not so bad in contrast.