Well I say that I am vegan, I often get reactions like:
“But you look so healthy, how can you be vegan?”
“People need meat to stay alive”
“People need to eat meat to do athletic things”
And I often get reactions like:
“So that is why you are so healthy/thin” (many people conflate health and thinness)
“Oh, so you do it for health reasons
“Wow, your diet must be so healthy”
So there are people who are under the impression that veganism is inherently unhealthy and that all vegans must be sick or dying or dead (I have asked people to explain the last one since I am a living vegan, and they have no choice but to acknowledge that their argument is absurd), and there are people who think veganism is inherently healthy.
The thing is … I do not think veganism is inherently unhealthy or healthy.
Obviously, it is possible to be healthy and vegan – every vegan who is in good health proves that it is possible. It is even more obvious that it is possible that is possible to eat meat/dairy/eggs/animal products and be healthy, since there are even more examples of very healthy people who eat animal products. There is so much variety in both vegan diets and omnivorous diets that I do not think it is even possible to judge that one is healthier than the other.
I think it is possible that vegans in the United States, Europe, and Asia are healthier than their omnivorous counterparts, but that would be because vegans have to be more careful about their food. It is being careful about food, not the veganism itself, which might lead to better health.
However, I think people want to make veganism about health or religion (the religion part comes up a lot in Taiwan), because if it is not about health or religion, then it must be about ethics.
I have spent all of my life in parts of the world where animals suffer horrible abuse. The vast majority of people are a) ignorant b) in deep denial or c) both with regards to the horrors they support by eating animal products. Either way, they are uncomfortable talking about it – people generally do not like having their ignorance pointed out, and are even more touchy about denial. If I am being vegan just for health, then it means that I am not challenging their (un)ethical stance on eating animals. If I am doing it for ethical reasons, and say so, even if I am super polite and never directly comment on the fact that they eat animals, they understand that I am challenging them on ethical grounds.