Meat is bad. Meat tastes good.

Let me just second Ezra Klein's post on this subject:

Bacon is transcendent. The words "porterhouse" and "steak" make my mouth water. Pork belly makes me simultaneously believe in God and doubt my own religious tradition. And because of this, I'm not a full vegetarian. But I should be. And not liking liberals don't change the truth about meat: Industrial agriculture is cruel, meat production is a huge contributor to global warming, and the market for meat contributes to world hunger in a substantial and direct way.

How does meat production contribute to world hunger? Because it's just about the least efficient use of agricultural land, in terms of its protein yield:
So all the land currently devoted to raising cattle (and there's a lot of it) could feed a lot more people at much lower cost if it were devoted to wheat, rice, soybeans, etc.

The problem is a classic prisoner's dilemma. Everyone may know that the world would be better off if we each ate less meat, but so many of us find eating meat so pleasurable, and one of us giving it up would make almost no difference to the rest of the world. We're not going to give up meat voluntarily. The government will have to play a role here. Good luck with that.