For me, personally, I agree that the industrial meat industry is unethical and has to go. My push-back against the herbivore claims is purely from an objective standpoint. Putting aside objectivism, if humans are omnivores, it makes the moral argument stronger. You'd be telling people they have a choice and can choose to eat a more compassionate and ethical diet. (More energy efficient, too.) If people are herbivores, you get stuck in this weird argument about what humans are supposed to do instead of what we can choose to do.

I spent a lot of time as a vegan, and talked about my choices openly. (Stopped on account of health.) No one attacked me for them and it was because I stuck to irrefutable facts and never made the person I was talking to feel bad for their choices. I just showed them they could easily be a better human, if they wanted to be. Maybe that doesn't feel like enough for you, but I felt that no one ever changed their position on a personal matter because someone else made them feel attacked. They always dig in their heels.