The assumption in every culture I've lived in has been that eating animals and their byproducts is not only acceptable, but the right thing to do. That is the default; the "presupposed" belief. But, it is a belief that requires no evidence to be accepted by the majority of people.
When shown evidence that animals experience suffering because of this behavior, and when shown evidence that animal agriculture is disastrous for the environment, you have evidence on which to make decisions from an ethical perspective, and not merely a cultural history perspective. What you do with that evidence is up to you, of course; the law will likely never, in our lifetimes, be strict enough to prevent animal suffering or environmental catastrophe. So, it's your decision to participate in it, or not, and to what degree.