: we don't go killing animals for food so they should not be killed for it either. You can get plenty nutrietion from other things. Just give them a chance!
Assume everyone switches to vegetables, all slaughteries become bankrupt and suddenly there`s not sufficient crop for everyone because of a new plant disease or drought (whatever). What then?
McSpotlight: Well, there wouldn't be enough to feed the animals either; a total failure in grain production would wipe out the meat industry as well; and there are a whole range of diseases which can only spread from livestock to humans (in fact, it's where most of our infectious diseases come from). So a vegetarian diet is not only more disease-resistant, it's also less fragile; since it depends on nothing but environmental conditions.