Defenses of free speech, up to and including free speech absolutism, are sometimes centered on axioms like “sunlight is the best disinfectant”. The theory goes that it’s better to expose bad ideas to society, so that society can kill them outright, rather than hiding them away, and letting them fester and grow in darkness.
But this presupposes an open system, where sunlight is always capable of overpowering infection. Or, said another way, it discounts the externalities of exposed contagions. It’s one thing to imagine there’s a moldy plate in the middle of your sunny backyard, but another thing entirely to imagine a completely polluted ecosystem. Those ruined landscapes require more than sunlight. You can’t just treat the result, you have to stop the causes.
There are classes of speech that are, to abuse the metaphor, a lot more like ruined landscapes than moldy plates. The rise of ethno-nationalism and race supremacy in western democracies is certainly among them. Relying on the disinfecting power of exposure is naïve to the point of being immoral. Society doesn’t disinfect the disease, the disease infects society.
We know now that blind application of free speech as a doctrine merely cedes the public square to the extremists, and results in a shittier society. Those with the power to do so have both the right and ethical obligation to stop these infections at the source, by organizing, by protesting, by de-platforming, and by recognizing that free speech isn’t an end in itself, but merely a means, a tool, which we’re obliged to use to make our society better.