Here's a real world example of why you shouldn't ride the wrong direction: I was heading down a one-way street in the bike lane and I saw a girl on a bike entering the intersection ahead of me from my right. She had a green light and turned right to enter the bike lane. Coming up the wrong way was an old dude on a bike. She came within inches of smashing right into him. Luckily she had skills otherwise it would have been ugly.