Veganism is a philosophy and way of living which seeks to exclude—as far as is possible and practicable—all forms of exploitation of, and cruelty to, animals for food, clothing or any other purpose.

If you include humans the philosophy part turns in to just utilitarian philosophy. There's nothing necessarily wrong with utilitarianism, but diluting vegansim, a philosophy opposing oppression of nonhuman animals by human animals into "being against bad things" seems a bit weird to me. Like if someone insisted that anti-racism is about opposing harm done to a person of any race. Sure, it's bad when white people harm marginalized white people, but it's not what anti-racism is about...

I dunno, I have a bunch of those little reasons why it doesn't sit with me and seems shortsighted.