Ever drive in a massively populated area? Driving at a safe distance is nearly impossible. Try it and watch how many nuts nearly kill you as they swerve around and cut you off. Driving in NYC or probably any other major city is a good example of this. Its not smart to ride the bumper of the car directly in front of you but, it isn't always possible to drive one car length per 10 miles or whatever consensus is the appropriate distance.
Whats worse is people who stop dead in the road and side swipe you when you attempt to pass them. Also slow drivers in the fast lane and anyone who doesn't use a blinker. Included are people who drive way below the speed limit and refuse to allow the 10 cars behind them to pass. Some people drive way to slow for the road. This encourages tailgating. I say if your gonna drive slower than the posted limit than at least let everyone else pass. One does not have a right to drive slow and if you obviously aren't in a hurry then get out of the way.