Humans are omnivores. We have the ability, structurally and chemically, to digest a variety of foods - plant and animal. We derive nutrients from both. That multi-functioning has helped us to survive millions of years of migration, treacherous weather, different environments. You have to love how industrious we are.
I think meat plays a role in a healthful diet. I don't think that role is big. And I think it varies from person to person.
Strict vegan diets provide some nutrients in such low amounts that it's best to supplement. Vitamin B12 and zinc come to mind. I have reservations about a diet that requires supplementation to be adequate. Why not get your nutrients from food?
However, the amount of meat humans as a whole (especially in the West) are currently eating is not good for the planet. If it's not good for the planet, it's not good for us, because we have to live here. Those two are inextricably woven. We have polluted ground and surface waters, increased incidence of foodborne illness, contributed to global warming, and placed millions more people at risk for hunger and malnutrition - all to satisfy our appetite for meat.
I think we're entering a time when the arguments over whether saturated fat (or protein or iron) in meat is good-or-bad will give way to the arguments about how much meat can be sustainably produced at all (and so, how much there will be to eat).
P.S. - The way we produce meat these days, resulting in cuts with more omega-6 fatty acids (not good), more organic pollutants, antibiotics, hormones, maybe E. coli, maybe prions (we don't test for mad cow), pushes me towards the lower consumption end too. And anyone who thinks large confined feeding operations breed happy cows doesn't give a whit about animal welfare. It's not that meat is inherently unhealthful, it's that we're making it so.