The boundary is crossed if I call you names, or if you call me names,
something a fellow poster seems keen to do to anyone who consumes meat,
or is a vegetarian consuming animal products, and can stand up and
justify their position. I would correctly describe him as a fanatic.

I don't think there's a perfect diet that works for everyone. We have to find what works for us. I *became* a vegan rather than being born into it so I've been able to tune my diet accordingly.
I predict within 30 years people in the western world will have practically stopped eating meat because of the push for sustainability and alternatives developed that are so similar that nobody will need to eat meat.
It'll be become like smoking. It's quite rare to see people smoking cigarettes these days, at least in the city I'm in.