it doesn't justify joking about factory farming
yes it does
especially when "hitting from above" and siding with the stronger opponent.
Firstly, punching down doesn't make something unfunny, it just usually is unfunny. When I do it, I find it very funny, and so do a lot of people in the audience. Secondly, I'm making fun of vegans, the farm animals are just collateral damage. Thirdly, they don't count because they aren't human beings. Fourthly, there is nothing wrong with siding with the strong, otherwise we wouldn't be allowed to make jokes at the expense of people like pedophiles and Nazis, who are on the fringes of civilized society and reviled by all.