I am of the opinion that "humans" have always eaten meat, indeed our closest "living" relative (chimps) often hunt cooperatively for small monkeys, however meat is not part of their staple diet. in other words they (chimps) will eat flesh when they can, but they do not depend on it.
Meat is also eaten by all sorts of animals previously thought to be pure herbivores, although they do not "hunt" even Deer have been observed eating carrion.
Personally the reason I stopped eating meat again (I was raised vegetarian but started eating meat at 15) is because although I made great efforts to only eat "organic" meat, I came to the conclusion that even animals that have been raised in the correct (imo) way, still have to go to a main "abattoir" for slaughter (legal reasons I believe) and I do not trust that they are treated with respect, the only power I really have is over what I buy or dont buy, so for now at least I am not going to eat meat*.
One other thing that often pisses me off is when people/morons claim to be vegetarian only to tell you that they eat fish. I mean WTF fish do not grow on trees they are creatures, and to make it even worse fish seem to be exempt from any ethical consideration about the suffering caused by the way they are dispatched, what I am trying to say is that there are laws in place that dictate they way that livestock should be slaughtered, so how is it legal that fish are drowned and or gutted alive? you would be wrong to think that nobody has thought about the "proccess", because fishing gear has been "developed" to cause less "damage" to the catch i.e. better condition of fish = better price at market. It would be more humane to electrocute the fishes before proccessing but that would increase costs. Then we have the issues of bycatch, over fishing and the pollution of
our seas.
It breaks my heart when I visit a supermarket and see the amount of "wild" fish destined for the bin (trash u.s). Don't get me wrong I find the amount of farmed meat thrown away disgusting, but those animals were not "taken" from the wild. (sorry for my rant

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*this might change when they have mastered "in vitro meat" (lab grown meat).
After thought: I also find the idea that vegitarians are wimps hilarious (just think shao lin monks and Alexander the great etc)