Vegans are the ones that think it's immoral. It's like the joke goes, how can you tell if someone is vegan, because they will tell you.

Vegetarian is just a dietary preference.

Vegans have more to do with morals than vegetarians. Vegans may refrain from using animal based products like leather, which can be completely unrelated to health. A vegetarian diet is just that, a diet without meat. Can be for health or moral reasons, unspecified.

Many things are tasty, many of which don't have the detrimental implications of animal products, especially meat.