>Assuming a well-functioning democracy, they have whatever rights The populace wants them to have, including deciding what types of speech are acceptable.
So... mob rule.
That seems like a very stable and restrained society. I can't think of any obvious problem with that, or any time in, say, German history (to name a particularly egregious example) where mob rule run amok destroyed most of the Continent. Or Russian history. Or Cambodian history. Or Chinese history. Or...
The only currently reliable way to defuse mob rule is to decentralize. This is done by passing laws that say that society can't stop its individual members from doing certain things. And while this does lead to a very polluted commons (and sometimes isn't sufficient on its own to prevent the mob from taking over), it also leads to an exceptionally stable society simply because the "we should gang up and hurt/ban the people we hate" reflex is impotent outside of one's chosen groups and the hands-off attitude becomes ingrained in the people after a while.
The right to be wrong is important, because once the mob decides that your life itself is wrong (or rather, the closer the local Overton Window is to that idea- the more entitled a society is to restrict its members, the closer it is to this by definition) you're in trouble as soon as the mob hits a rough spot. It might advance faster at times, but it's just too unstable.