I wonder if the people who say to not do this have ever actually worn headphones while riding? I used to wear headphone on my commute but just found them uncomfortable so I stopped after a few weeks.
I very rarely ride on MUPs (Multiple Use Pathways - jogging trails) so I'm riding in the street with vehicles. When I'm not climbing all I hear is wind noise, and the sound of cars behind me. There is absolutely nothing that my sense of sound has done for me to keep me any safer. I can't tell which lane a car is in, or how close they are until I can see it. Headphone will at least cut down some of the wind noise, and in areas that have less tolerant people yelling out the window you may not hear them as easily - both increasing safety and enjoyment.
If you're really concerned about safety use a rear view mirror.
I very rarely ride on MUPs (Multiple Use Pathways - jogging trails) so I'm riding in the street with vehicles. When I'm not climbing all I hear is wind noise, and the sound of cars behind me. There is absolutely nothing that my sense of sound has done for me to keep me any safer. I can't tell which lane a car is in, or how close they are until I can see it. Headphone will at least cut down some of the wind noise, and in areas that have less tolerant people yelling out the window you may not hear them as easily - both increasing safety and enjoyment.
If you're really concerned about safety use a rear view mirror.