vegetarians definitely live longer and healthier (studies of seventh day adventisits in the 80'd). production of veg foods is easier on the environment than meat production. veg food production is also more efficient, so more hungry folks can eat off the same amount of land than if meat were produced. and of course, it sure is easier on the creatures with faces we now consume.
drawback is it's hard to get your B12 as a vegan, so this must be supplemented. the most potent omega-3's are also fish-based, so you might want to consider two wild salmon meals per week to get your share of the proven omega-3's.