I also never understood why fans of other teams get abused for simply following another team. The way I see it, they are the same as us. They are supporting their local side, just like we are. They just happen to have been born in a different town.
I think that often football rivalry is exaggerated to the point of being manufactured, in order to give some people an excuse to vent their non-football related frustrations on something other than the actual source of those frustrations (unsatisfying job, unhappy marriage, whatever).
I love football and BFC but I cringe at what some of our fans sometimes say. That's to be expected though. Football has universal appeal and as a result you end up socialising with people who you might normally avoid. It's healthy for us to come out of our respective social bubbles periodically, but it is of course not without its frustrations.