If I would eat plants, I would eat the food of animals and possibly kill them. That is why I think it is better to eat meat.
I don't know are animals intelligent. But, I think many humans are not intelligent either, I think it is not a good reason to eat them.
I think eating plants is no more climate-friendly than eating animals. Possibly it is the opposite. Plants grow on CO2 and they produce O2. Killing them is bad for environment, if we believe CO2 is a problem. I think it is not.
I don't believe animals have souls. But, I believe they can suffer and that is why, if people kill animals, it should be done in a way that doesn't cause much suffering.
Biggest question for me in vegetarianism is, how to get B12 vitamin. It seems to be difficult to get it, without eating meat and by what I know, the vitamin is very important.