Humans can choose to be vegetarians of course, that doesn’t mean that killing animals is immoral or wrong, necessarily. That notion can only exist if you think humans have a superior place in the world to that of animals. Anthropocentrism is central to this idea that humans are the only animals who cannot kill other animals to feed themselves without it being immoral.
Ie a chimp could choose to eat fruits if he wanted but they also often eat monkeys even if fruit is available. How is that different, from a human choosing to eat a cow even if he could eat grain? The difference is only that you think the human “knows better” than the chimp.