I wish this was true but in Germany, Belgium and holland uttering the opinion that the holocaust didn't happen (an idiot's point of view but an opinion nonetheless) or minimizing the jewish holocaust in any way will land you in jail. Racism is a crime in Belgium for which you can be fined. Other mass murders (soviet, chinese or Turkish genocide of Armenians) can be denied to your hart's content. This is of course an extreme example but the slippery slope always start at the extreme end.

You cannot have a democracy without free speech. Hate speech legislation is the slippery slope to tyranny, because opposition and opposing arguments are the lifeblood of any free society. As soon as you start criminalizing the other's opinions you lose that very necessary but intangible principle. Once you start designating certain opinions as wrong and unutterable lest you go to jail you've started on the path to tyranny.

And the really nice thing about that definition is that every lefty is still free to praise Stalin and Mao and call for the immediate death of everybody who owns more than somebody else or who has the audacity to make a better than average living through investing in or running a profit making business...