Well, not while on a moving bicycle perhaps.

For me, I shake my head at riders who are crankin' the tunes ONLY because I can't believe they don't appreciate the sound of what's naturally around them. Much of my cycling nirvana comes from the sounds that are all around. From the smooth chorus of the crank spinnning the chain around to the whir of the spokes to the tires rolling smoothly on the ground... it seems like you would lose that connection between us, the bike and the road.

But, do what you want. I'd never vote for a law banning headphones on the bike - or even a law requiring a helmet. It's your choice; do what you want!