You can eat most meats raw so long as it’s fresh. The truth is though, that even raw veggies aren’t properly fully digested by our guts and we don’t always get the full nutrition out of them just because our guts are so short compared to a true herbivore. Humans evolved into what we are because of cooking. It gave us smaller jaws and shorter guts and enabled us to eat a variety of new exciting things we couldn’t appreciate before. Now that we needed less energy to consume and digest raw meat or plant matter it freed up some valuable real estate in the head area.
Huge jaws became smaller and more delicate where the brain and cranium became larger and more complex. Unfortunately our gut also became kind of wussy and now cooking our food is nearly a necessity.
You can eat raw meat if it’s fresh but some animals carry stuff your stomach acid isn’t strong enough to kill, and you can survive on nothing but raw veg but it’s more work because you’re gonna be pooping most of those nutrients out.
I assume you mean raw meat. After all, many people eat raw fruits and vegetables with absolutely no problem.
You can eat raw meat fine as well. The problem is that it’s very easy for microorganisms to grow on raw meat. It needs to be cooked or prepared correctly to reduce that risk.
If I remember my biochemistry correctly, cooking meats also frees up some proteins/amino acids that our digestive systems wouldn’t be able to process otherwise. This isn’t enough to cause “stomach problems,” as most people use that term, though.