Honestly, it's people who also completely ignore the evolutionary requirements of a human diet. I'm thinking of people who obsess over carbs like they're some kind of poison, or the nutjobs who think that humans can and will do just fine as carnivores or fructivores.
When I first went vegan, it was for health reasons. I'd had an accident and I fucked up my guts pretty good. Gluten and meat, and even dairy and eggs were literally hurting me to consume, so I had absolutely no choice in the matter. I'm better now, but it was a rough couple of years.
I remember this one vegan YouTuber vividly. He was insisting that eating nothing but fruit had been good for him, that this was what a healthy human looked like, and everyone else was crazy. I just looked at this dude with his sallow, papery skin and gaunt frame, and I just went, "Ooookay, great incentive to start adding things back into my diet as soon as I'm healthy enough to handle them again."
By all means, be vegan. I think it's genuinely a great idea. If you can't, then be vegetarian. It's also a great idea. If you can't do either, then just be sensible and eat less meat. But ffs, take a good look at the people who fell so far down the rabbit hole that they look like living ghouls, and pay attention to the hard science and good common sense.