I had a vegan roommate for years. I didn't cook much meat when he was in the house. But I was never personally vegan. I also did agree that it's more ethical to not kill for your food, let alone all the other horrors of factory farming. And I'm able to accept that I don't live up to that more ethical standard.

I think maybe people just don't like to think someone (especially annoying people) might be doing something better than they are? Like you said, special insecurities.