It's not about not being able to imagine the need or not. It's from seeing people driving their cars at highly dangerous speeds all the time (easily 20mph faster than most people who are already driving 10-15mph over the limit). If it were only dangerous to the driver, it'd be one thing but they put others in danger. There are countless stories of speeding drivers killing bystanders.

No one has ever a need to drive at 120+mph.