As I've shared many times before, I'm an ethical vegetarian. People have different reasons for choosing vegetarianism, some do it for religious reasons (which I believe are still based on ethical principles), as well as for environmental and health reasons.
Personally I think it is great to be a vegetarian for health reasons, but it is also a selfish approach, because it is about what it does for you. Being a vegetarian for moral reasons is not selfish, because it is about what it does for them. When I try to get people to embrace vegetarianism, it is not about me. I stand to gain nothing. Ethical vegetarianism is about animal rights.
If I hadn't become a vegetarian for moral reasons, I would have done so later on when I found out the environmental impact of meat, because I'm also an environmentalist. Again, doing it for the environment is not a selfish act. Not that being a vegetarian or vegan for health reasons is bad, the animals and planet still benefit, but it is an act that does not involve morality. I also think it is easier to fall back to old omnivore ways if you have adopted the lifestyle simply for personal health reasons.
Morals are about the motive or intention behind doing something. It is about doing the right thing for the right reason. Which brings me to my next point. I've been watching a series of free online Harvard lectures on justice. They are quite interesting and I highly recommend watching them. If you only have the time to watch one lecture, check out the one where Immanuel Kant and morality are discussed.
If you have the time, watch all 12 lectures in the series. While they are not specifically vegetarian or vegan in nature, the information relates to the choices we make in our lives. It's a free Harvard class covering justice, ethics, morality, etc., and you can't beat that! Access the classes here.
Check out this video showing what the Harvard Justice course is all about: