Personally, I think responsible, courteous people are that with or without headphones, and those who aren't courteous people are the same with or without headphones.
I do wear them on the railtrails - I wear them when it's not busy (and it rarely is when I go). I don't enjoy listening to my own breathing, it simply makes my mind think about whatever problems are on my mind and that is REALLY distracting to me PERSONALLY. Nobody sneaks up behind me, I have a mirror. When someone approaches me from behind, I physically acknowledge them so they don't have to guess whether or not I know they are there. I keep my head up, I look around, if I look like a victim with them, I'm going to look like one without them too - I'm not spacing out and watching my tires roll. I've heard the deer rustling before they've wandered onto the trail with my headphones on - and they are the most likely obstacle I'm ever going to run into on these trails.
I've been stuck behind (usually men) on a leisurely ride who are yapping with each other riding side by side that I can't pass. No, they don't have headphones on, but I guarantee they are far more oblivious to their surroundings than I am.
I don't ever wear them on public roads. I wouldn't wear them when the rail trails are busy. I have been treated far less courteously than I've ever treated anyone else on the trail --
Bicycling is the number one reason for the increase in the ranks of reckless girls who become outcast women" ....unknown 1895