WOW!!!!! I didn't think this thread would be so controversial. I am one that does wear headphones (in one ear ,the one away from traffic). I felt bad after reading all the post ,and went on a 10 mile ride in" Beaverton" traffic without a headset on. My mind was so pre occupied by all the thoughts of the day ,and just thoughts in general. My concentration level was low. I know I'm more aware of traffic while wearing a headset. It may not work for everyone ,but it works for me. I ride to the right of the bike lane ,and turn around every so often to make sure no one is behind me. I can hear cars very well. I never wear them when I'm riding with someone. I wont wear them next Sunday on my 40 mile group ride.
You talk about the sounds of nature , birds etc...well the sound of wind can block out the sound of traffic. A head set helps with the sound of wind.
Suzie