I can't do the marxism/vegan view justice myself in one post, but from the theory sub if anyone actually cared to read it:

Marxists, in turn, do not hold animal liberation activists in particularly high regard either: they are often seen as strange ascetics and bourgeois moralists who invest themselves in negligible causes instead of focusing on the key issues. They are expected to take part in actions and alliances for class struggle, but to leave their ‗animal craze‘ at the door. Many comrades break out in cold sweat when they ponder a society in which both humans and animals alike are liberated from exploitation and oppression, since it would mean giving up their meat and cheese. And anyway: Friedrich Engels already made fun of the ―Herren Vegetarianer‖ who underestimated the importance of meat consumption in the history of human civilization and who were, at best, utopian socialists.

Nevertheless, we reject this opposition and believe that the historical materialist analysis and critique of society developed by Karl Marx and Friedrich Engels, the corre- sponding politics and the call to liberate animals from their socially produced suffering all necessarily belong together. On the one hand, demands for animal liberation are indeed moralist if they do not analyse the historically specific conditions in which the exploitation of animals is taking place and which social changes are necessary to end it. On the other hand, however, every Marxist critique of society remains incomplete if it does not consider the fact that, to make profits, the ruling classes have not only exploited the oppressed classes within the history of class struggle, but also and always animals (and nature).