Well, to a large extent it is indeed true that you shouldn't trust people who disagree with things you think obvious. So there's a sort of "conservation of smartness" going on, whereby you need to be smart already in order to collect a few "obvious" beliefs that you can then use as your litmus test. So for that person, if they really do think veg*nism is obvious, they might be "doing the best they can" in rejecting LW for that.

FWIW, I'm not a vegan anymore, but I'd agree that any attempt to "minimize total suffering" would have to include not eating meat, ceteris paribus. So anyone who claims to have that goal but still eats meat is either a liar, or suffering from some sort of "intra-self disagreement", or they believe ceteris is not paribus (e.g. "eating meat somehow lets me work harder on saving the world"), or they're uninformed. (Or something else.)

Protip: type '\*' to make a '*' symbol without LW thinking you want italics.