Computer studies of traffic patterns have shown that a slight increase in the average following distance, compared to current averages, allows traffic to better handle sudden changes in speed cause by human error.
So the, OPPS I almost missed my exit, sudden braking and lane change is far less disruptive when safer following distances are maintained. The multi-car accidents that often result from tailgating are far more disruptive than increased following distances.
This particular study is on lane designs to reduce tailgating, but every study of tailgating comes to the same conclusion. It is dangerous and causes far more traffic problems than people think it solves.
http://www.dot.state.mn.us/trafficeng/tailgating/Tailgating-finalreport.pdf 
