Undoubtedly some folk like to drive fast regardless, and often inappropriately so, but in my experience the majority of people don't drive 'fast', but adequately to the circumstances.
That is to say, a majority of drivers will drive at 75- 80 mph on motorways when the conditions and traffic are right. That might be above the speed limit, but in the right circumstances is neither fast nor wrong or dangerous.
But the same drivers will drive well under the speed limit when they feel the conditions dictate so- for instance doing 50 on a 60mph road if traffic is heavy or weather not good. In such cases they're not driving slowly- they're adapting to the circumstances and driving at an adequate speed.
We need to recognise that just as some laws are wrong and it is okay to challenge and break them, some traffic laws are inadequate and it is not irresponsible or wrong for drivers to break them. Modern cars are infinitely safer and better performers than the Morris Minor in which the current speed limits were set. There is nothing wrong with exceeding the speed limit on motorways or dual carriageways if the circumstances allow it.