I've been a vegetarian all my life until now. This is because I am stuck up in the following holier than thou sentiments:
(a) When I can eat well without causing pain to sentient beings, why should I go out of my way to cause pain to sentient beings? It's not like I am starving on lentils, veggies and beans and the like. (I have made some more progress on this viewpoint, contending that eating free-range wapeti and salmon (for instance) would probably be okay with my code of ethics - because that's the way of nature. I still have not eaten any wapeti, rabbit and free range salmon yet - because of lack of opportunity, and significant pushback). My issue is with industrial farming.
(b) With each animal taking a significant amount of energy to raise, can a world with 9 billion (projected) people really afford to feed animals that are slaughtered to feed the rich? Animals in the US get better food than lots of Indians. Since each kg of meat takes more than 200% of the energy a corresponding kilo of vegetables, meat is an unnecessary luxury.
(c) Since each kilo of industrially raised meat takes more energy than a corresponding kilo of vegetables, certainly meat farming emits more CO2 (and methane). This is fairly unequivocal: The planet is warming because of human-related emissions and deforestation. Meat is guilty.
If they manage to do away with issues (a) through (c), then I would definitely eat meat. And it looks like it might every well happen soon. In-vitro meat is just around the corner.