Coincidentally I did have an IRL conversation with an older comrade about this topic (I've been a vegan for 5 1/2 years now) and she told me to read a passage from Engels that he wrote about vegetarians (the part played by labour in the transition from ape to man) in dialectics of nature.
Thinking that I couldn't be the first to be a vegan communist to read this, I found this great blog: https://medium.com/@lilligroeneveld/challenging-friedrich-engels-about-veganism-2c17f303a269
Great read, basically sums up all the same thoughts I had and then some!
Imo: Reactionaries always admire the barbarism that the rulers were capable of in feudal times and the trope of "everything will get better with the right leader in place" appeals to the idealism of liberals.