It isn't 100% natural, but the omnivorous diet that most non-vegetarians eat nowadays is much less natural.
In the distant past, in hunter-gatherer societies, the reality was that the vast majority of people's diet came from plant sources, i.e.gathering food, with a relatively small proportion coming from hunted animals.
It is only in the last 100 years or so that meat has come to make such a large proportion of people's diets.
If we were meant to have a primarily meat based diet, we'd have mouths like dogs, rather than just a few pointy teeth.
The thing about protein and vegetarianism being a problem is a bit of a myth though – as long as you get a varied diet, you can easily get enough protein. For example wholemeal bread has 10g of protein per 100g, so you can get 10% of your 50g just by the bread on a single sandwich.
In terms of globalisation and environment, the impact of meat farming is massively massively more, as it is a very inefficient way to create calories or protein. That is why there is an environmental movement for people to pledge to not eat meat for one day a week (or more).
Joe