When you stop doing what you like/love, it's a huge decline in quality of life.
Overlooking whether vegans or religious sects are good, bad or whatever, what really happens is probably that people find other vegan people, become part of a community and enjoy that.
It's the same cargo cult process that makes everyone want an Iphone. I dread the day when a high percentage or, god forbid, majority of people start looking down on those dirty meat-eaters because "won't anyone think of the animals?".