If I may comment on the main thread topic:

Distraction when operating a vehicle is bad, but not every distraction is equally bad. Actuaries, legislators and other people with an interest in risk actually quantify distraction and discover facts like: texting while driving is more dangerous than dialing a phone number while driving, which is more dangerous than changing a station on the radio while driving, which is more dangerous than simply listening to the radio, which is more dangerous than not listening to the radio... And so on. At some point along this spectrum we separate things that shouldn't be done from things that are OK, and we write laws or enact mores forbidding the really bad things.

I think that listening to earbuds at a low volume certainly dulls the senses, but in many cases (i.e. as long as you aren't in really busy bike or car traffic) it sits a ways down the distraction spectrum, certainly below the threshold of things that shouldn't ever be done.