I used to think this way. Former vegans of almost 3 years.
It is not the animal flesh. Is the modern food industrial complex. THEY want you sick. We have a thousand years of history and human eating patterns to study to prove that meat is not harmful to the body. Refined carbohydrates, hydrogenated oils, copious amounts of processed salts, and sugar are the main culprits for the adverse effects we experience. The human digestive system is robust enough to handle a variety of diets, but the nutritional deficiencies found in many of these diets (plant-based or other) are why many dietitians advise incorporating one from the other for balance.
I am mostly plant-based, which comprises about 85% of my food intake.
For me, it's mainly eggs, fish, nuts, seeds, fruits, legumes, and vegetables--chicken gets thrown in intermittently.