It is in fact very easy to be a leftist and a not a vegan.

1) animals aren't people
2) even if they were, not all people deserve to live
3) Meat tastes good
4) it's possible to raise and slaughter animals humanely
5) Moralizing is reactionary

Veganism, particularly the brand that seeks to normalize itself, is a bougouse neurosis that places the suffering (real or imagined) of animals over humans.

As a human who interacts mostly with humans, I care more about the happiness of humans than animals.

Is this cruel and arbitrary? Would it suck if some alien decided to eat me? Yes and yes. We live in a world where predatation is inevitable. If I don't draw a line between humans and animals, I must then chose whether or not to draw a line between animals and micro-organisms.

Even if it was possible to objectively define what constitutes a life form capable of suffering, it would still be impossible to behave altruistically to every single organism in existence. Even vegans have to admit they prioritize some animals over others.

All life exists to be food for another life form, the only difference is how and when it dies. I will agree with animal rights activists that factory farms are a needlessly cruel way to "produce meat." but I can't sign off on the life denying idea that nobody should be food.

Industrial agriculture in general is wasteful and destructive. Western veganism simply trades factory farms for factory fields and congratulates itself on a trivial reduction in waste. If that's all they really want, they should focus on vat grown meat instead of moralizing.