The 18th-century revolutions that were centered around fundamental rights of man, were pretty hostile to monarchy. France famously guillotined supporters of the monarchy. Even the USA tarred and feathered loyalists or drove them into exile in Canada or the Caribbean. It was only years later, once monarchy wasn’t a realistic possibility any more (or, in France, the public mood had come around to monarchy again) that such advocacy was permitted again. And then later movements for instituting a non-democratic regime, namely fascism or communism, got various degrees of prohibition. So, I’d say it’s pretty normal even for successful democracies to interpret fundamental rights in that light.

I am happy to allow for any state transition that allows for a peaceful reversal of the event (i.e. an undo button). If it's a monarchy, it should be a monarchy with guardrails (i.e. could be deposed by a snap popular vote with 2/3 majority or something)

If the plan of the people, once in power, is to prevent any challenges to their power, we should not run such experiments, and those people do not deserve free speech rights.

Free speech has that paradox unfortunately built into it (see Karl Popper's Paradox of Tolerance). Universal free speech is a pipe dream you wouldn't enjoy living under.