Don't need to hear horns? You see, the thing about driving with headphones is that more people do it than we realize. Only most of them can't post. THEY'RE DEAD!
Hearing car horns has SAVED MY LIFE on numerous occasions. God gave us more than one sense for a reason! WE NEED THEM ALL! Hell, if you were just risking YOUR life when driving, I'd say go ahead and put on headphones. Blindfolds too, if the bright lights bother you. The problem is, when you drive you risk MY LIFE! And I'll be damned if I want my life in the hands of someone stupid enough to completely block one of the two senses needed to properly operate a motor vehicle! There's a reason driving with headphones is illiegal in most states, and if I see you doing it, I'll sure as hell report your ass to local authorities!
I remember I was coming through an intersection one night, and the railroad crossing sign didn't work (giving no indication of a train, in the dark of night). FORTUNATELY I WASN'T WEARING HEADPHONES! How can you tell? I'm STILL HERE!
Then there was the time a kid's basketball bounced in front of my car (from between two parked cars, so I didn't see it), and a second later, the kid behind it. FORTUNATELY I HEARD THE BASKETBALL HIT THE PAVEMENT, braked and swerved just in time to save the little fellow's life.
"Don't need to hear when driving". Indeed!