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.

I don't know. I find the people insisting that farmers are the same as pedophiles to be pretty infuriating personally.

I conceive the freedom to chose on a personal ethical base above the idea of punching down ideas just because.

I agree it's a choice, but I don't think it's a personal one given that there is another sentient being victimized in the action.

A bit on the motivation behind vegan activism:

Say you're against needlessly exploiting animals. And you purchase/produce animal products when there are other options available. You would be needlessly exploiting animals while affirming a contradiction, that would be hypocrisy. Nobody can force you to act on that, but they can point what you're accountable for.

Vegans believe that most people are against needlessly exploiting animals, so they try to show this to people. Confusion may get in the way, but wanting to put on the spotlight what kind of exploitation people are supporting is what guides them.