The problem isn't when you're tailgating, the problem is when you're comfortably cruising at 80 mph and all of a sudden you realize there's a stopped car in your lane. It can be surprisingly hard to notice the one car that isn't going with the flow of traffic. There are videos of cars getting totaled this way. Not sure I want to know what happened to the passengers.

On busy highways, if your car breaks down and you need to slow, one of your biggest concerns should be to get out of the way asap before someone rear-ends you.

Whether you consider it a result of tailgating or not, pile-ups are a common result of unexpected action on a highway.