If your plan to save the world includes requiring all 9 billion people to fundamentally change their lives (especially if its perceived as a degradation of their current quality of life), it's never going to work.
Now I'll speak for myself. I will not go vegan, given the current offering of vegan foodstuffs. It just doesn't taste as good. I know it may be better for me than my current diet, and I know it could help decrease my overall carbon footprint. I still have no plans to do it.
Perhaps it makes me greedy. Perhaps it makes me an asshole in the eyes of the next 20 or so generations. But I look at it in the larger context - the ship has sailed, our course towards permanent (on a human scale) climate change was set by the industrial revolution and the speed set to flank by global increases to our quality of life.
So yeah, I frankly refuse to permanently sacrifice my quality of life to have no effect on the future.