The problem is that the concept of free speech cannot be independent of the concept of power. Rules and Laws are only as good as the people in power choose; we've been lucky in many ways that most of the time, the people in power choose to behave in a way that upholds the laws that we consider important. However, that "good will" is specifically what malicious actors exploit in order to achieve that power and then violate the same rules that allowed them to spread their message and come to power.

And unfortunately, once they have power, there is very little that normal people can do to ensure that they will obey by the rules that got them there (i.e. free speech). I would argue that there was no way to prevent the Nazis from squashing free speech except by preventing them from coming to power - and this is true with many malicious actors. Unfortunately, that means we have to balance the need for free speech with the need to prevent malicious groups from coming to power.

Ergo, the Paradox of Tolerance.