because people usually meet deviation with resent. Same goes for all alternative lifestyles. i say fuck those bastards, they're just jealous that they can't control their urges to match their own ethics, so they eat abused animals all day, but give their dog a bath right afterward. Make any sense at all?
Because lots of vegans come off as being morally superior simply by rejecting stuff others would eat. Whether they are preaching or not, picking and choosing what goes on your plate is a very political act.