There’s very little that one should be disallowed to say.
As long as one’s words are not directly causing harm to non-consenting others, there should be no limits, unless the person voluntarily locates themselves in a place where limits are imposed, in which case they should abide by the limits.
Shouting “FIRE!” in a packed movie theater (when there is no fire) is not free speech and should not be (and is not, in my place) allowed. This action will cause the place to evacuate, people could get hurt in the rush out, and there is no actual emergency. Direct physical harm is caused by these words, this infringes on other people’s rights.
Swearing in the post office is tougher. By entering the post office, you agree there are things that should not be done, and you agree to abide by entering and participating in society. Such as pooping in the middle of the floor, causing physical harm to others, etc. Swearing is generally not acceptable as a part of civilized society. If one keeps it to themselves (muttering to oneself), this should be fine, as it causes very little harm to others. But shouting obscenities, that is affecting other people who did not explicitly consent to hearing your shouting, and should not be allowed.
Inciting riots, again, what is the intent? If it’s to cause immediate harm and damage (ie, after a sports match at the bar, you rile up the crowd to do rioting), I would argue that this type of speech should be monitored if not controlled, as physical harm to non-consenting folk will come from it. If it’s a group of people sitting around talking about any type of non-supported concept (overthrowing the government), as long as there is no action towards doing so, I believe there is more harm in stifling such discussion than simply allowing it.