Sheep sometimes eat birds and eggs. Wolves sometimes eat vegetables. Naturally eating a variety of food is quite normal - “vegetarian” primates depend on accidental insect consumption for some of their vitamins.
But if a sheep eats too many eggs, or a wolf eats too many vegetables, they’re going to get ill. Their bodies are adapted to specialise in certain types of food, and don’t cope well with the side-effects of other foods.
For instance, meat turns nasty in a long digestive tract. Meat eaters have short powerful digestive tracts to get the meat in and out as fast as possible. Humans have long digestive tracts that process slowly. Meat rots in us.
Humans aren’t designed to cope with modern “western” diets. We can eat it, we’ve traditionally eaten it, but our bodies haven’t caught up. I don’t believe that we’re profoundly different from other animals, that we have the bodies of herbivores but somehow are suited to meat eating via our hands and brains. Our hands and brains simply enable us to obtain a diet we’re not capable of processing safely.