Providing a platform where people who subscribe to these kind of ideas can self-organize, and connect to demagogues who would lead, them is not a virtuous defense of freedom of expression; it is a real threat to the liberties and lives of the people these ideas target.
Submerging people in sealed bubble of misinformation that only reinforces their prejudices--as Facebook does through a combination of advertising, recommendations, and control over user timelines--does lead to radicalization and that radicalization can be weaponized in ways that are fatal to others.
Just as the right to swing your fists ends at someone else's nose, the right of 'bad ideas' to be amplified by platforms ought to end before people who believe in those 'bad ideas' are turned into political weapons by demagogues and would-be autocrats.