The following video is imo an excellent summary of the cognitive dissonance that allows humans to do or condone bad things while viewing themselves as good people. This not only applies to how meat eaters justify killing animals unnecessarily, but also to other areas of human activity where we kid ourselves that we're not doing really shitty stuff...
Mic the Vegan is one of my favourite vegan youtubers. His videos are informative, well referenced, not too long and I like his content, presentation and humour.