Even when I ride a freewheel bike, I only ever use the front brake. I would occasionally use the rear brake to scrub speed, but the front brake is where all the stopping power comes from. I never felt like this was bizarre or put me in any danger. The back brake I just did not use. I run only a front brake on my fixed gear, though I rarely use it. I tend to skip to stop 99 times out of a hundred. I keep the front brake for emergencies.