There is no proof that the central nervous system is responsible for sentience. Mowing a lawn is a mass extinction event for the residents of that lawn. Does a broken grasshopper suffer less than a broken human, simply because it can't wax poetic about its experience? Veganism promotes monoculture and environmental destruction as well, it's just easier to pretend that it doesn't.
My point about personal comfort is that it's the ONLY metric by which you measure your moral code regarding consumption of other life forms to extend your own life.
While we can't be completely sure, our current understanding of sentience makes it a reasonable assumption. Even if plants are sentient, eating from higher trophic levels causes more plant deaths than eating plants directly.
Regarding the rest, I feel like I addressed all of that in the comment above. I'm a fallible human being and personal discomfort with killing animals no less cognitively complex than our pets, and sometimes toddlers, is definitely a factor, but I've been arguing based on necessity and quantity instead of that.
EDIT: And to be clear, I've never claimed veganism is environmentally perfect. It doesn't solve every problem with food production, it just helps with some, and it seems largely better for the environment (albeit with nuance around grazing certain types of land) even if we keep doing monocultures.
If by that you mean both sides were civil, ty haha. I'm trying not to replicate the toxicity of the average reddit argument (which I got sucked into a lot) but I worry I still get too logic-as-my-blade, so I'm glad if my intentions still got through.
A great tip I've heard is to try to read others' comments in the most good-faith tone possible, since it's easy for that not to carry over text.
Yeah civil but also just a higher level conversation overall. And in a place like /memes. Just reminded me of old reddit. But maybe I just like logic-as-a-blade convos lol