Support for vegetarians means helping us look good in the eyes of non-vegetarians, by cluing us in to some of the stupid things we say, that non-vegetarians recognize as being stupid. Knowing the stupid things some vegetarians say, can help make sure we avoid saying such stupid things.
Like... vegetarians never get sick.
Or... you can't find vegan food in... Mexico, Louisiana, Montana, or some other place where agriculture is abundant. When what they really mean is that they can't find 100% vegan choices is restaurants, or frozen prepared food in supermarkets, and have to resort to preparing their own dishes, from basic agricultural products. If they had said Tibet, or the sahara desert, I might believe them, but who is going to believe Mexico?
Supporting a vegan doesn't mean agreeing with them when they say I can't find vegan food in Mexico. Just like supporting a pro-choice person in being pro-choice, or making the best choice for themselves, doesn't mean agreeing with them when they say an embryo in a woman 12 weeks pregnant is just a mass of cells.