Rather sweeping generalisations there! On what facts do you base these statements?

Based on the number of terrible drivers I see speeding on the roads every day. The aggressive drivers, the tailgaiters, the people who change lanes constantly and weave in and out of traffic, the people who don't signal, the people who cut other people off. You don't see the people who are going the speed limit doing these things, for the most part. Most, if not all of the people who do these things (with the exception of not signaling and to some extent, cutting other people off) are people who are speeding.

People who speed are usually impatient people (which is why they break the law on a regular basis by driving significantly over the speed limit). An impatient driver is a dangerous driver. And I think an argument can be made that if they regularly break the traffic laws, that, in itself, makes them bad drivers.

There's plenty of bad drivers who don't speed as well. But the fast drivers are more dangerous, because the faster a car is going, the more damage there is in the event of an accident.