I approximately go by Bentham's criterion for what makes humans morally significant: we can suffer, as can animals. Rocks cannot. There is no reason to believe one configuration of a rock is "better" for it than another, as it has no kind of mind. I see no reason to believe a plant has any kind of mind either.

A pig, however, does prefer some states of reality over others, to quite a great degree. I think it's reasonable to say that the conditions we raise most pigs in mean their lives are a net negative: they'd be better off experiencing nothing than experiencing the lives and deaths we create for them.

I suggest you've tied together two questions. You're working backwards from "I'm going to keep eating meat", and have wound up at a conclusion that animals must not be morally considerable, because of that. Instead, separate the issue into two questions:

1) Are animals morally considerable? Is there anything I can do to an animal that is unethical? Is it okay to kick a dog, if I gain some momentary amusement at listening to it yelp?

2) How should the trade-off between my benefit and moral consideration to others work, exactly?