Most nations besides the US don't subscribe to an unlimited right to speech. Hell, the US doesn't subscribe to an unlimited right to speech.
Should I be allowed to say that I think you should die for the opinion you just espoused? That is probably not a legal statement for me to make under the US principles of free speech.
Should you be allowed to say that you think I should die for my genetics or the social group that I am born into?
Glad we've agreed that while free speech isn't bad because some people say bad things, that doesn't mean that all free speech should be legal, either.
As we've thus agreed, we can absolutely restrict certain categories of speech without diminishing the actual social value of free discourse.
This idea is entirely uncontroversial in every single developed country except for the US. Nobody else thinks that "well I just want to murder all the jews but you want to suppress free discourse, looks like you have some growing up to do" is a valid position for people to take.
No, that's not polite to say, but that's where your argument ends up, and that's really the entire purpose of that argument. Otherwise - what arguments exactly do you feel could not legally be expressed in a modern first-world democracy, that actually should be expressed?
This argument literally, always comes down to someone who argues that "well I don't actually (openly) support Nazis marching in the streets, but I don't think they should be legally suppressed from expressing their desire to murder an entire race of human beings". Again, otherwise, be glad to hear what exactly you think you think people have a problem with that is legally suppressed in the communist state of Germany or Sweden in 2019.
The reality is that the laws are always interpreted by humans and a huge amount of deference is given to free speech in all but the most explicit cases. Yes, if the system becomes corrupted we have a problem, but that's literally always the case even with an unlimited right to free speech. There is no slippery slope here unless things go completely off the rails, and things can always go completely off the rails under any system.
We really, actually, can just ban the Nazis marching in the streets without everything magically turning into a dystopia. Germany has done it for 75 years.
I realize you probably think I'm overreacting because this idea always went over well at your college smokeouts, but I'm under no obligation to sugar coat this for you, I'm just being blunt: this is an occasion when your opinion is trite and shallow and you really should re-think the consequences, because it's entirely possible that your opinion gets people killed over the next decade. You're not Atticus Finch for white-knighting the right of Nazis to express hate speech.