"Funny" is subjective, so pointless to argue about that. Of course it's oversimplified, it's a web comic!

As for the vegetarians, those who do it for ethical reasons ("Singer, in his book Animal Liberation listed possible qualities of sentience in non-human creatures that gave such creatures the scope to be considered under utilitarian ethics, and this has been widely referenced by animal rights campaigners and vegetarians.") certainly consider sentience an important factor.

The author suggests one simple metric: minimize sentience/calorie, and makes a pretty convincing argument, as webcomics go. You know, an actual calculation, not just emotions. Seems like a much more rational approach than demonstrating against killing baby seals because they are aww so cute.