Very good points... intuitively, rail seems safer (and simpler to automate?), but your points have changed my mind... Now I wonder though, how do modern roller-coasters stop so suddenly? Magnetic breaks?
Electromagnetic brakes are used, but the biggest difference is that the weight of passengers is a much bigger portion of total weight (you don’t have a locomotive and the cars are not nearly as heavy per passenger) a decelerating quickly is part of the appeal. If passengers on trains were unencumbered with stuff and strapped in as on roller coasters, they could be built to do it too.
