This implies that people have the ability to withhold this power from government. If they can do that, they can ensure that government enacts limitations on speech in a reasonable, proportionate and acceptable way.
Not so. The power of the state is blunt, and restrictions must be equally blunt. Put it like this: a fence can keep a fox out the pen; but try telling it which chickens it can attack once it's inside.
I'm fully in favour of limitations on speech. Not only do I think they're inevitable by one means or another, but they're actually desirable.
Well I thank you for your honesty.
The qualitative distinction between a despotic and democratic society is false. It's a matter of degree. Most rights are stripped "for the public good". (French Revolution, to name but one.) And it's a politician's perception of "the public good", anyhow too nebulous a concept to be of any practical use.
Pornography isn't expressing an opinion, hence not a matter of free speech. Harassment
can be an issue of free speech if the law's used to regulate the content of words, and the US Supreme Court strike down such statutes: but if you're stopping people hassling a specific individual, you're not regulating the content of their words, just their target, so again, not free speech. Incitement to violence is again not an opinion; it's an action (an attempt to commit a physical criminal act by proxy). It's no more a free speech issue than a soldier ordering a massacre would be.
No, people are not immune to speech, but our entire legal system is predicated on the idea that people be expected to control themselves, and any criminal act is done by choice. If people are so feeble that a wicked idea can override that control, then all sorts of totalitarian policies are justified.