> I think it mostly has to do with other people's insecurities. If I say something like, "veganism is unhealthy" (because of lack of B12... yes I'm aware there are nuances), some vegans interpret that as a statement of opinion, rather than a statement of fact, or even as an attack on their lifestyle choices, because they are so involved with their egos.

I'll bite. It's true that a vegan diet can be unhealthy, and that it's wise to supplement with B12, but that doesn't mean a vegan diet is unhealthy.

This is like saying "an omnivorous diet is unhealthy because you don't eat enough vegetables". Sure, some people with omnivorous diets need to eat more vegetables, but that's not true of all people who eat omnivorous diets.

I'm not sure whether you would benefit from increasing your precision or accuracy, but the "veganism is unhealthy" line is plain wrong.