sxz: +1 for headphones.
Its no worse than someone cranking their stereo.
I too use headphones sometimes to listen to audiobooks, have on my bike a few times as well. The volume is low, the headphones are not noise cancelling or blocking, and I can hear ambient noise just as well as anyone else. If you can be distracted so easily you should not be driving!
I disagree, wearing noise cancelling headphones means if you aren't paying attention your not going to hear / see emergency vehicles. I see it as a total disregard for other peoples safety.
At least someone with a loud stereo system is more likely to hear the air horns of a fire truck or the buzzer of a police car or ambo.