To add onto your already excellent answer, another reason that going vegan for purely health reasons doesn’t make sense is that, as you said, veganism isn’t a diet. Or more specifically, the ethical stance that is veganism includes more considerations than just food. Someone that eats plant based foods only may not care about things like leather or other animal products that they may use on a daily basis that aren’t part of their diet. That person wouldn’t be vegan, but rather simply eating a plant based diet. I don’t mean to be pedantic but that is the distinction between being vegan and eating a plant based diet and there is no reason to be entirely vegan for health reasons alone unless you want to take it to the extreme and say that you don’t use animal products like leather because the animal agriculture industry creates pandemics and contributes significantly towards global warming. Despite those being perfectly valid (and important) reasons to be vegan I think that it’s a bit of a stretch to call those personal health reasons.
I’d also just like to add that nutritional yeast is a great source of vitamin B12 and is naturally vegan.
Obviously we still have political protesters and things like that but nowadays things are so divided politically that it is typically a topic that you would avoid in everyday conversation. If you were to bring up anything political with your coworker at a get together after hours for example and you find that you are on opposite ends of the political spectrum it could make it very difficult to work together at best and potentially endanger you at worst.