I think he's saying harming a human being is morally worse than harming an animal, all else being equal. I was confused as well but I think it's just the Community meme wording. Had to reread it and look up the actual line from the show.
The line is "I can excuse racism but I draw the line at animal cruelty". I'd forgot the extra layer of irony, that it's a white woman implying cruelty to animals is worse than cruelty to black/brown people.
This fucking site strains my reading comprehension sometimes.
being murdered on a factory farm
I think a factory farm slaughtering people is considered outside the realm of possibility. I assume the vast majority of people would consider that morally worse.