The argument that neo-nazis don’t go away by making their propaganda illegal has been put forward many times, and I consider it to be a trueism. But the alternative approach, making it legal to wear the Nazi cross and to openly deny the holocaust, wouldn’t make them go away as well.
I, for one, don’t believe that they have more success due to laws restricting denying the atrocities committed during the third Reich.
Defining at which point my free speech violates the human dignity of others is difficult, and has sometimes to be discussed. But I tend to accept that my freedom ends at points where it causes harm to individuals, or groups of people, or society as a whole. (The latter is the most difficult to define, however, I think it might be important to remember). Racial slurs, directed at a specific person as well as directed at the general public, do cause real harm. And protecting minorities is an important societal achievement.
We can easily discuss if blasphemy laws, the weird lesè-majestè laws we just got rid of in part and several other laws protecting the actual majority, or those in power, are good for something or should be dumped. But in case of racial slurs?
No, sir.
That said, I come back to my geo-referenced disclaimer: unlike the US, most of continental Europe has law modelled on the French Code Civil. This leads to important cultural differences when discussing free speech, I think. Given that Twitter and Facebook, and all the other, smaller platforms, are US companies also culturally, this leads to problems. Attempts like the recent “lex Twitter” in Germany are quite short-sighted and obviously motivated by the upcoming elections, but I wouldn’t dismiss them as total garbage, and decidedly not as censorship. It’s a feeble attempt to motivate the companies to get their shit done in the language they might understand: money.
But don’t get anyone with a law background started on the matter; I guess it’s not worth the paper it’s written on.
However: it’s written. And there you have it. Cultural difference. You might call it anal, I call it the rule of law. 
