Fallacious yet widespread and documented beliefs courtesy of Wikipedia.
A vegetarian or vegan diet can provide enough protein. In fact, typical protein intakes of ovo-lacto vegetarians and of vegans meet and exceed requirements. While lower in protein than non-vegetarian diets, adequate but low protein diets have been shown to be beneficial against cancer. A non-vegetarian diet high in protein such as a typical diet in the United States in fact has been shown to be linked to several diseases including osteoporosis, cancer, impaired kidney function, and heart disease.