To be honest, if that's what concerns you, discussion forums like Urban Toronto are no better.
Besides, given how FB is structured, there's a simple solution: don't bother with a group like I Hate The War On Rob Ford. Don't engage them at all; or, let hardier (or foolhardier) opposing souls do so instead.
Though an interesting observation from a rare I Hate The War On Rob Ford visit on my part: the threads there seem to be an endlessly circular flashback to the days of Usenet or the early 00s warblog/discussion-forum era, almost as though all the participants are all still working in their pyjamas on home computers with tube monitors...