As one who does not care if the food i eat has meat in it, maybe i can clarify why people react like this. It's simple: you make me feel like i'm some sort of a heartless, evil person for eating meat, i will make you feel bad as well. Eating chicken is murder ? We humans are omnivores, we eat anything. Meat is less efficient land wise, but is more efficient to digest. Morals have nothing to do with it, as we have long evolved to be that way.

If you want people to eat more plants; my advice is to make it a better option. I often make myself a 100% plant pasta sauce, but that takes 3x longer to do and doesn't cost much less then just grilling a piece of meat and cutting a tomato or two. Make cheap tasty vegetarian fast food stalls, cheap mini markets, etc. Calling people murderers will make some of them hate you.

PS I have a vegetarian friend, for over a decade i didn't know he was. Respect his decision, has nothing to do with me.