Even in a world where everyone is vegetarian or even vegan (but remember that this wasn't always the case), this is still a somewhat funny joke. I, e. g. don't eat meat, but found it hilarious.
This kind of reaction is what they allude to in the Matrix when they say "if he's not one of us, he's one of them". You are already ready to fight to defend a system of slaughter and oppression.
It's all word views. Obviously a Christain who believes in souls has no reason to respect an animal if it doesn't have one.
But, I just think we are matter, so I imagine that matter inherently experiences. In that case, humans are no longer the obvious protagonist who has no reason to feel bad about abusing the rest of those out there.
Edit: And the fact that racism likely comes from people looking different, acting different, having resources we want, difficulties in communication, and/or leaders having an incentive to support it, it is pretty easy to see how specism exists. Whethere or not you care about that is up to you.