Because by eating animals one consumes more plants by proxy. That being said, getting eaten is a core part of many plants lifecycle. Same is true for a lot of animals, but to a lesser extent. On particular for domesticated animals this argument falls apart a little. But they still exist to be eaten and are advantaged evolutionarily if they are good at that. Adverse effects like diseases and pollution do exist.

I mean plants do communicate distress, so I can see that. While we haven't evolved to live solely on sunlight, suffering will happen. That we are aware and only take what's needed, with respect seems correct.

10/10 ragebait

Some people are gonna give you grief about this, but you raise an interesting point. I was just talking about this the other day with my gf and my son over a vegetarian dinner we were having. There is more and more research about plants be more intelligent (for lack of better word) than we thought before. Still kinda taboo in science circles, but it is being discussed and looking into.