I've been vegan for around 6 months now, and haven't dropped dead yet. If anything, I feel the same as I did before - on a vegetarian diet - and before that - on the standard Western diet.
As long as you eat a balanced diet with enough protein, fat, and carbs humans can thrive on a vegan diet just fine.
How many super overweight people do you know who eat all vegetables and whole grains?
There are always outliers but the cliche western 'bad diet' is too much meat, fat, processed carbs and dairy.
I'm a reluctant part-time vegetarian - pizza is my spirit animal. But I cannot ignore the cognitive dissonance I experience with a lot of the 'bargaining' style diets being pushed. My animal brain really wants to believe there is a healthy diet that lets me pile on the bacon and chorizo and still lose weight but the evidence just doesn't support it.
Too much refined sugars + animal products = fat population.
The only nutrients "missing" are B12 and D, which are easily supplemented and/or found in fortified foods (cereals, plant milks etc). And the funniest bit - they only exist in meat because they are supplemented into cow feed. That's right - you're already supplementing D and B12.
I don't know where you're from, but where I grew up meat was an occasional food. The diet was mostly vegetables/fruits/grain, with meat from hens/ducks once a month or so, cows and pigs were slaughtered right before winter so there was more meat during winter but still for a family of 5-8 that's like a serving or two a week.
IIRC that's the standard diet for millennia - mostly plants but still occasional meat.
I don't think humans are made for vegan diets, but the current consumption of meat is absurd - we're eating better than kings and nobility used to.
How is it possible that meat can be cheaper than vegetables, it's rather ridiculous. Industrial farms are quite literally animal Auschwitz, yet people don't see the problem with that because they're "just animals"? Funny how that works.
I think slowly raising taxes on meat would gradually lower demand, and soon enough, production. Can't see us getting off meat completely, maybe lab grown will be successful.