I don’t buy the “we are top predator” argument, either.

First, we should note that this argument means we can kill any creature we want, including cats and dogs, and also that future evolved man and extraterrestrials can kill and eat us if they choose. I doubt that if you were on the receiving end of that that you’d be okay with it.

As human beings, we’re only as powerful as we are now due to our big brains and ability to craft tools and weapons to force others to submit to our will. Strip all of that away, however, and you stand no chance against a lion, tiger, bear, ape, elephant, rhino, etc. Hell, a lot of us are afraid of spiders and mice which doesn’t speak very well to our top predator image. :)

At its core, though, what this argument is really saying is that might makes right, which holds very little weight from a moral perspective. This has been made clear from the numerous atrocities that humans have committed against each other throughout our history. I think it’s high time that we move beyond that level of thinking.

As for the “other animals eat other animals all the time” part of your argument, I don’t see how this is relevant to morality. There’s a host of activities that wild animals engage in from copulating with members of their own family, infanticide, and defecating out in the open, yet these are not the sort of behaviors that we’d cheerfully adopt ourselves. No, we’re just selectively choosing which behaviors we want to model for our own convenience and peace of mind.

As for the plants argument you brought up, there is no solid evidence to support their sentience. But let’s just say if they were proven to have some degree of sentience, it still takes many times the amount of plants to feed oneself through animals than it does to eat plants directly, so instead of just eating the plants ourselves, the suggestion is that we should kill many times more plants to feed the animals, plus then also kill the more highly-evolved animals as well? That is hardly an effective argument for eating animals. In fact, it is a highly effective argument for not eating animals.

At the intuitive level, we of course already know all about the categorical difference between sentient animals and non-sentient plants, because if we were ever given a bunny, a carrot, and a knife, it seems pretty safe to say that unless we were a psychopath we would cut the carrot and feed it to the bunny. And we also intuitively know about the minimization of harm principle as well, because if we thought that carrots were also sentient but we were being forced to stab either the carrot or the bunny, we would still choose to stab the carrot rather than the bunny.