Firstly, I really want to stress that human beings are NOT meant to eat meant(Naturally). You can double check this with any biologist. It can be told from our teeth structure, which indicates the kind of foods our body was meant to eat, and meat is NOT one of them.

Secondly, meat is not just killing animals, but also killing us! Every year, to meet the consumers' demands, lots of animals are brought up. The first problem, is that the animals will have to get food from plant sources(usually), however, cutting down greens will mean that there are less plats removing carbon from the air. Secondly, animals also give out alot of methane, which like carbon dioxide, enhances the green house effect, contributing to global warming.

On the other hand... well, its true... eating meat has become part of our life, so taking meat away is, and will be a difficult task.