I'm in the absolutely no headphones camp. People who say they are fine and can hear everthing since they don't turn their headphones up very loud or wear one earbud belong in the same camp as those who drink and then say they are just fine to drive in my eyes. They don't understand how dangerous they are being.
It IS possible to rely on your eyes for safety - deaf people do it all the time. People without earbuds in can be riding and not paying any attention either - spacing out in their own little world, worrying about whatever is going on in their lives.

When I was a zookeeper and was always running heavy equipment or loud hoses, you just learned to be alert with your other senses.

You know, it seems that many here aren't even tolerant of those who might ride for leisure - even those who are respectful of others, move over when faster traffic comes, even pulls off the trail or road. I suppose that just opens a whole other can of worms though.

I don't know where you come up with thinking that trail riding is inherently more dangerous than road riding either, that one just totally baffles me.