People are ignorant. Whether it's about vegetarian diets, history, or how cell phones works (seriously, have you seen those ridiculous "time travel" memes, where they claim people in old Hollywood movies had cell phones??!!!)...I'm a voracious reader, and I certainly don't know everything, but I encounter constant frustration with people who are blatantly willfully ignorant...it's because there's this chunk of the population who never read nor research. ..they rely primarily on TV or folk wisdom for the formation of their opinions. ..these people are a blight to me, they get on my last nerve, while I'm only of average intelligence, they make me feel like Einstein walking through a crowd of illiterates...
I have had to learn to change the subject, tell people I don't want to talk about this, and to stop reacting to people on the Internet. ..because the Internet is now just as rife with ignorance as the irl general public.
It's hard. Especially when it's something you strongly care about, like being a vegetarian.
But I think we grow as humans when we learn to rise above these people mentally. I'm still very much working on how to do that.
The primary thing I have gleaned is that it's seemingly endless, and only a few here and there are actually interested in the information you offer, so why argue.
It doesn't help that we currently live in a culture where all or most opinions are called equally valid, when some are clearly more ignorant or less humane.