I could feel safe at 100 mph if I was the only car on the road, and I had tires that were designed for that speed, and I knew that the car was perfect mechanically, and there were no deer, moose, cows, sheep or horses crossing the road, and the road was as straight as an arrow.
I've never doubted my ability to drive at any speed, but my ability is a tiny part of what is required to drive that fast.
Just yesterday here, a whole family was wiped out because some sap fell asleep at the wheel, crossed the center line and hit another car head on. It happened too fast for the other driver to react. That is only one good reason that 100 mph is too fast.