Well, that’s a completely different argument.

If something is wrong, then it’s wrong, regardless of how efficient or inefficient it is.

How much earlier are we talking? I bet if you asked prehistoric hunter-gatherers whether they thought animals experienced pain, they woulds say yes. The idea that animals were automata comes from Descartes.

What? The fact that plants physically react to being cut has absolutely no bearing on whether they have conscious experience.

How about I just get to eat meat because I consider it far more humane to be more efficient about proteins?

What does this have to do with anything? This is bringing efficiency to an ethics fight.