"Oh Shit" moments...

Worst case; your chain breaks you hurtle down hill into a petrol station, hitting a young woman refueling her fiesta and spilling fuel on the floor, as you slide out, now horizontal, your pedal hits concrete hard and sparks fly from it. The spilt fuel ignites into a ball of flames, sending debris far and wide and a cloud of thick smoke into the air. This cloud disrupts a plane which dives into the nearby nuclear facility at Aldermaston. The resulting meltdown kills most of south east England, but not before missiles are fired out to all corners of the earth, triggering secondary launches from other nuclear powers and destroying most of the life on earth. All because you think having no front brake looks cool.

That would be pretty darn bad