Some of our roads with 60mph limit are woefully inadequate to justify that kind of speed; on the other hand, 70mph on a clear dual carriage way or a motorway is a 50-yr old nonsense - even in my city car I can do 110mph safely ....
Most people can do high speeds safely - and if you were an F1 driver, a judge would let you off a ticket based on your occupation.
However, what the judge fails to consider is that an F1 driver is doing stupid mph on a track where everyone else is going in the same direction. Everyone else has had the same high standard of driving tuition. Everyone else is driving a state of the art car which is maintained at every opportunity.
Nobody is joining from a slip road. Nobody thinks they are there to police speed limits. Nobody has to worry about joining a queue of cars trying to get by the two lorries overtaking each other. Nobody has to worry about all the debris from badly maintained cars (not to mention the grease from split CV boots, the oil from gearboxes, sumps, diffs etc).
Nobody has to worry about the kid who has just passed his test or the granny who is blind as a bat or the driver who has just come here from abroad. nobody has to worry about the rep doing stupid mph whilst closing a deal on his phone & writing out an order - all whilst keeping his foot flat to the floor...
Nobody has to worry about the driver who can't see out of his window because the map is in the way.
With great freedom comes great responsibility - and sad to say, a great many drivers simply cannot handle responsibility - probably the main reason why speed limits have remained unchanged.
And whilst modern cars have far better braking systems, you are still talking about propelling well over a ton of metal along at stupid mph with no more than a couple of square inches of rubber in contact with the road. Even with ABS, assisted braking etc etc, laws of physics still cannot be ignored.