I can't decide if this is a genuine post, or whether it's a troll trying to get a rise out of people (both pro- and anti-vegan). In case it's real, here is my opinion:

I am Jewish, vegetarian, and have some serious food allergies (the kind that lead to anaphylaxis). All of these things have a significant effect on what I eat. I don't make a big deal of it. I don't judge what or how others choose to eat. If I'm invited to someone's home for dinner, I ask if I can bring a dish in addition to a bottle of wine. If I am going to a restaurant, I check out the menu online ahead of time, and if there isn't anything I can have, I just eat first and have a drink and nibble some bread while people have their meals.

Being social is such an important part of being human. If you choose to ostracize yourself over your beliefs, that's kind of a sad option.

There are always options. I am neither vegan nor vegetarian, but I have friends that are. Some of them are so insistent that everything has to be exactly the way they want it that they refuse to join in any event where everyone isn’t either vegan or vegetarian. So fine, they’re not coming. The reality is that we live in a complicated world and that means that we can either learn to adapt, or opt out completely. Adapting would require that you tell your hosts that you follow a specific diet but that you will bring your own main and would love to come to enjoy the company. If you can’t handle that, then I suggest that you’re going to need to get used to being alone a lot.