Well if it changed your habits then I would say you shouldn't have to watch the last 2/3rds, because that's the whole point of the film being made in the first place

Other than that, it should be mandatory viewing. It angers me that people won't watch something like Earthlings because of how it makes them feel. Uh cows are being chained to the floor and dogs locked in tiny cages like something you'd see in the most sadistic of torture chambers, yet you're worried about how YOU feel?