For me it's primarily the texture. I do like the flavor of onion as long as it's not overpowering. Cooked or not, biting into onion is like nails on a chalkboard but on my teeth. If it's chopped up small enough or powdered I don't have a problem. When my wife makes food with bigger pieces of onion, she makes them big enough that I can pick out.
For a long time, though, I would just say I don't like onion and try to avoid it altogether.
Mine's a blue bunny.