Actually, the only omnivore that got on my case for my diet was my grandmother. And in her case, it definitely wasn't anything about vegetarianism - she would have screamed at me just as much if I'd announced that I was eating nothing but rare steaks for the rest of my life. It was about control and making me feel bad.
She straight-up stopped speaking to me about anything except my diet, yelling about how I was going to slowly starve to death. I weighed "be constantly harangued about diet" vs "have father grumble about how I'm a bad grandchild for not talking to her" and decided to cut her off.