[drewbuschhorn]

You could make just as a valid (and philosophers like Popper have) that allowing unfettered free speech has also led every society that tried it down the road to dictatorship.

Dictatorship is one of the easy to find local minima of human organization, that we have to fight everyday not to slip down towards. You do that by accepting the humanity of your opponents, finding reasonable compromises, and there's no reasonable compromise to be had with the Nazi ideology, just ask the dead.