Vegetarians historically did it for ethical reasons. Pythagoras because he believed animals have souls, Plato too, Benedictine monks ate fish because fish don't care for their young so the parents won't be upset if you eat their children (!), etc, etc.  Even Alex Gleason does it for ethical reasons.

YET epidemiological studies show vegetarians living a very long time, and it's pretty obvious when you know a lot of them (I grew up a Seventh Day Adventist, many of my ancestors lived to about 100), and track health gurus and see the vegetarians living past 100 but the meat heavy promoters dying in their 60s.  I've got a huge list of people, it's super obvious, but people just refuse to accept it because IMHO they like to eat meat, so their active brains construct reasons and logic to defend this position... which is the common backwards way most people think.

I'm not saying a little meat is bad.  It isn't.  Pure vegetarianism has problems with iron, B-12, protein quality, and probably other things.  That's why I'm not a vegetarian.

And while I agree with Pythagoras that animals have souls (that is to say, they are conscious aware beings)... they don't after they are dead.  After they are dead, they are meat, which is good as a food.