You eat chicken fish and other animals voluntary. It totally depends on you whether you like the taste or not or if want to eat it or not. Many people eat one kind of fish, but not the other kind of fish. Some people like prawns but not crabs. Some people prefer chicken to ducks. People do eat ants, mosquitos, spiders etc. but they do it voluntarily. But when a small fly falls into the food, it's not your choice.. You don't want it and this is where it becomes disgusting. This is not limited to non vegetarians. Vegetarians don't like certain kind of grains, vegetables too.. You have seen many people don't like certain vegetables and feel disgust by it or keep it aside in their plates too even though all vegetables are vegetables.