It can decompose for example muscle and other connective tissue (which actually is quite important to be healthy), but it does limit ability to build tissue.
Lesson from bodybuilding crowd is that you need to eat protein with every meal if you are serious about building anything. They want to build muscle but it really extends to all tissues of our body.
I have nothing against veganism and vegetarianism. It is a lofty goal.
But strictly on health standpoint, no amount or kind of plant food can (currently) beat healthy whole animal tissue (you should really eat more than just meat and also not all animals are same way healthy to eat).
Now, this doesn't mean there can't be better plant-derived foods in the future. A protein is a protein is a protein.
The problem with plant based protein is they come in wrong concentrations, wrong combinations, they are missing some stuff or they have extra things that make protein more difficult to absorb. If we can fix these points, we can have healthy plant based diets.
But really the main benefit of meat is that you get close to the right concentrations of everything by very definition. If you eat whole animal, that is. We have evolved to eat meat and only evolved to eat plants to supplement some small things (mainly vitamin C and to eat fructose and alcohol to get fat for the winter).
With this, any stupid person can eat relatively healthy diet. You just put a steak in your mouth and you are 80% of the way there.
On the other hand eating healthy diet on plants is a difficult task requiring planning and diligence that I think half of the population is simply not equipped with brain power to execute correctly.
We evolved as opportunists and generalists. Humans are capable of taking nutrition from plants or animals.
> and only evolved to eat plants to supplement some small things
I believe this is backwards. There are examples of hunter-gatherer societies with meat-dominant diets, but more typically hunter-gatherer diets were/are predominantly plant-based. In most environments hunting was a less reliable source of food and more opportunistic.
> But really the main benefit of meat is that you get close to the right concentrations of everything by very definition.
Not really. Maybe if you were eating chimp... but chickens have very different compositions to cows, pigs, salmon or polar bears.
> You just put a steak in your mouth and you are 80% of the way there.
It really isn't that simple. For example, it is well established that excessive red meat consumption raises the risk of colorectal cancer and other bad things.
Well yes but no. Large brains were largely made possible by the fact we mastered fire (mostly to cook meat). Look at gorillas, they eat plants and spend most of their waking life to forage for food. Having even larger brains means that foraging would be impossible to sustain a modern human's constitution.