Just because vegetables, lentils or nuts contain protein it doesn't mean it's the same/equivalent to the protein in an animal product.
Meat is actually super easy for humans to digest and it has no downsides to it. All vegetables on the other side contain plenty of anti-nutrients such as folate and oxalates.
Everything in human body, skin, connective tissues, tendons, hair, nails, muscles is essentially built out of protein and collagen. Fats are essential for hormone function.
In moderate amounts, sure. But frequently eating red meat (more than two or three servings a week) is terrible for you. There's "a clear link between high intake of red and processed meats and a higher risk for heart disease, cancer, diabetes, and premature death": https://www.health.harvard.edu/staying-healthy/whats-the-bee...