The problem is that these hate movements aren't necessarily linearly correlated to the level of free speech. If there is less free speech, then indirect speech, euphemisms, and dog whistles are used. It doesn't stop it. Once any rule is made, it can be worked around. Even worse, the additional rules often anger and energize these people due to a perceived feeling of persecution. And lastly, the rules always get misinterpreted and abused to shut down significant amounts of speech that should not have been censored.

Unless you can prove with certainty that free speech causes an increase in violence and death, then it's better to default to openness.

The KKK and white supremacists marched in their clown parades regularly for decades and we laughed at them. Is it a coincidence that their movements grew significantly with the amplification of messages against them and social media censorship against them. Various right wing figures used this as leverage to increase their virulence.