I think the assumptions involved in asking the question is wrong. Mankind can consume raw meat without incident, it just happens to be energy inefficient to do so and require pretty specific conditions to avoid food borne pathogens.
The GI system is host to a massive amount of bacteria, but they are relatively benign and help protect you from invaders, known as gut flora. The gut flora makeup of a being that eats a lot of starch based products is not compatible with the gut flora of a carnivore, so modern diets have stopped us from being able to eat raw meats.
The other reason is to do with the modern agricultural system, which tends to overcrowd animals (much more likely to cause infection), and the animals are not fed their evolutionary diet. To worsen it, industrialised evisceration tends to spew guts everywhere, so all meat has to be cooked to kill off any gut bacteria.
Whole muscle meats from carefully eviscerated animals, like beef can be left quite rare.
In Japan, chicken sashimi (think tartare made with raw chicken) exists and is safe to eat, but equally you're not advised to eat raw chicken from the supermarkets unless you want campylobacter or salmonella.