The number one reason not to ride is safety. I've heard that you are ten times more likely to die riding a bicycle then driving a car (no idea if that is adjusted in any way, though). The famous adventurer Steve Fossett said the only time he was truly scared was when biking the streets of Chicago.
I would ride the 13 miles to school in a heartbeat if I didn't honestly fear for my life in certain sections of surrounding suburbia. Riding across a bridge on a blind corner with no emergency lane in 50mph traffic is where I draw the line...
If only an extensive network of class I bike paths existed like the freeway infrastructure...It took me 40 miles of circuitous bike/street paths to get to a destination 20 miles by freeway. I think it's some kind of conspiracy...
- LostCause