The probelm isn't that all
activists are
annoying, it's that
nice people make lousy activists. Nobody has ever achieved anything major in politics by being
polite, and that's the sad and
unfortunate truth.
Especially in these days of hundreds of TV channels, radio stations, newspapers, magazines, e-zines, web-publications, newsletters, periodicals and pamphlets it is impossible to get one's message through the backgrounds noise without some kind of irritability factor. If you want an example from a completely different field, the footage of skeletal children in Ethiopia with flies crawling all over their faces are the shock factor that is used to stir people's numbed-down sensibilities into doing something about it.
It's very unfortunate that you were put off the message by the way this man was expressing it, but at least you are now aware of a problem, something that perhaps one day when you hear a better speaker will reawaken your enthusiasm.