Earlier quoted context omitted.
> And I do have faith that sunlight is the best disinfectant, and that truth will prevail over lies. I wish I had that faith but I think the Holocaust stands as a pretty big counter-argument. I'm genuinely curious about your faith, do you think that something could have been done in Germany in the 30s which would have preserved free speech and prevented the Holocaust?
The KKK was thoroughly defeated as a power in the US thanks entirely to the US system of freedom of speech; the KKK had a very large, potent base at one time. They were not outlawed as a group, sunlight-as-disinfectant overwhelmingly won out (and no, the US still having a small number of KKK members with next to zero political power isn't a good counter point). It was the ability to tightly regulate and limit speech…
While the Ku Klux Klan Act of 1871 didn't, you are correct, outlaw the Klan as a group, it did authorize a whole lot of measures—including authorizing federal military force and suspension of the writ of habeas corpus, and new federal civil and criminal causes of action—to combat their actions and those of similar groups, and those authorities were liberally used in suppressing them. Describing the successful strategy as “sunlight as disinfectant” rather than massive application of force is... not grounded in fact.