Why not? There are roads without speed limits, both public and private, and drivers capable of driving safely above that speed. Driving really fast doesn't happen to be my hobby, but I see the appeal.
You got the question I was responding to backward, it was said that there is absolutely no rational reason why cars should be able to drive above 150km/hr.
"Come up with some reasons why people wouldn't want to drive fast" is trite, boring, I would have ignored it.
Edit to clarify: "Why not" in my reply isn't "Why not drive fast", it's "You say there is no rational reason, why not? Here's one".