I don’t know if your second to last paragraph is a meme, but all humans reject immoral behaviors that occur in the wild, not just vegans. Lions also commit infanticide so their genetics carry on and competing male lions don’t, it makes sense biologically. Yet humans don’t commit this behavior because we know it’s wrong. Dolphins rape other dolphins, which again for the furthering of your own genetics makes sense. You should implant your seed in as many helpless victims as you can, and yet again, humans don’t do this because we know it’s wrong.
Pretending like vegans are the weird ones because we’re simply consistent about our morality is wild. Non-vegans even get upset at the idea of eating dogs or cats, so it’s not even like they’re universally in favor of torturing and slaughtering helpless animals, only the ones that have been objectified by whatever culture they live in.