Buckle Up Bumper Stickers

I've wondered why people put bumper stickers on their car which are supposed to encourage other motorists to wear their seat belts. One driver shouldn't want other drivers to buckle up due to the moral hazard problem. People will drive safer if they don't have a seat belt. Steven Landsburg proposes that roads would be the safest if there was a spear coming out of each person's steering wheel pointed straight at their heart. Taking away the spear and putting on a seat belt gives you a sort of license to drive more carelessly. You should want to be the only driver on the road with a seat belt.