First of all, health. In fact, my husband's cardiologist suggested he should go on a vegan diet, which means not even eggs or dairy products. While I am a vegetarian, I don't think even I could manage vegan. Cholesterol is found ONLY in foods of animal origin, so losing that from the diet is a huge plus. The body makes, on its own, what little of that substance is needed. Adding more from the diet is unhealthy.
We are not actually designed as meat-eaters, and it is not good for us. However, I realize that centuries of learned habits die hard.
Secondly, the environment. Did you know? More pollution and 'greenhouse gases' are produced by feed lots than by motor vehicles.
Thirdly, empathy for other living beings. All animals, not just humans, feel pain, sadness, love and suffer accordingly when they are slaughtered, and when their young are taken away from them.
I see no difference between eating a cow or killing and eating one's pets. They are all sentient beings.