This is not going to catch on. Entire industries, McDonalds, KFC, most fast food, and industrial farms - are going to be affected. But I surmise, having a meatless society could be a net positive for the environment as there would be less nitrogen and methane produced by animal poop. But then again, it would take an entire generation of people to get rid off their meat addiction. As somebody was apt to point out earlier, meat is an essential part of the human diet.
And by George, does fried chicken and tenderloin taste good!
Best solution that is still somewhat realistic in my opinion is to make smaller scale farming practices more commonplace. Happy meat is tasty meat, get people hooked on the better tasting meat and at least part of the humane issue cures itself. The scary PETA people will never be satisfied, but regular people can probably agree that commercial chicken practices for example are pretty cruel. Make the practices of raising meat less cruel and as a result more tasty, and then you just have to get over the issue of cost. Theres probably some solution there somewhere for getting meat from farmers markets under $10/lb and into the grocery store meat price range.