A phrase usually meant to incite anger among gay rights supporters or cheers from social conservatives. While it is true that there are some truly radical (and in my personal opinion counterproductive) gay activists it is unfair to tar all of them with this brush. For evidence of this just look at the Log Cabin Republicans. They can hardly be described as radical.
Using words like these (or other button pushers, like gun nut, mad Yank, pinko liberal, etc.) generally cause people to ignore other parts of the argument and proceed to either bash the speaker with blunt objects or carry him around on shoulders like a hero. Not terribly good for having a nice rational discussion, but excellent for sound bites.
Note: I didn't pick the name. If I were to talk about gay extremists I would just say Actup! members. (Surely you remember them. They were the <expletive deleted> group that "occupied" St. Patrick's Cathedral in New York.) I really don't like them due to the fact that they seem to have an attitude of "any publicity is good publicity."