I don't like things that add to noise pollution (such as speakers on bikes and/or motorcycles). I don't have a problem with other people wearing headphones while riding, though. I feel like you should be able to ride safely even if you can't hear, as long as you're paying attention.

I'm aware that states have differing laws regarding the use of headphones while driving or riding, but they usually allow for headphones on ONE ear, if not both.

Personally, I don't usually listen to anything while walking or riding, but I do like having a radio when in a car.