Sure. Why not just put blinders on too?
Actually it depends where one is riding. If you're on a deserted stretch of road or trail, why not?
I have a little Awia stereo that I bunjee on to the rear rack. It's the perfect size. Not a boom box. Small enough to pack away in my Camelbak. It delivers just enough sound to keep me company and not drown out what I need to hear. No headphones involved. A bike with a sound system. Pretty cool eh?