Adamantine

[dukealien]

The benchmark of tyranny

is censorship:

once the use of force

rises above the mark,

then even the censor

must drown in the flood

of ****.

In mild to moderate critique... not being a coastal dweller, I was thrown off at first by the reference to a "benchmark" - to a landsman, a benchmark (leaving aside its usage as a maker's mark on goods or a standard for evaluating interest rates, etc.) is a position reference like those placed by the Geological Survey.  Which includes height, but... perhaps an alternative is the Plimsoll mark on ships which shows the deepest they can be loaded before endangering the crew.

As for censorship, it was once a good thing... back in the Roman Republic, where forbidding distribution of written works was a minor part of the job.  Then, the Censor was responsible for keeping the lists of citizens, patricians, and senators.  If one misbehaved, he was struck from the list.  Now *that* is power, and when the Republic failed the office of Censor was corrupted like all the others - Dictator, Tribune, Consul, all assigned to the Emperor or his cronies (or his horse).

But for modern meanings of "censor," the poem has it right.  In the old sense, we lack a proper Censor to eject the immoral and vicious - and harness the rest to their proper duties, no shirking.  In the new sense, all the forces converging to censor - mob cancellation, doxxing, SWATting, malicious boycotts, denial of service attacks and collusive handshakes between government agencies and social media oligarchs - do have the goal of tyranny much as they try to hide it from everyone including themselves.

  Back to the poem.  The metaphor seems plausible:  abuse of power is the ****.  In the States we have a First Amendment which at least served as a sea wall which has taken centuries to undermine.  In Blighty, the  unwritten constitution shows its weakness today as pursuivants fan out to censor (in the worst sense) true speech which annoys the self-defined tyrant.  (Stay anonymous, @Strangerous, if you're a Blighter!  Speaking truth to power hasn't been this dangerous since the days of Cromwell.)

Final note:   the title could, perhaps, be improved - Adamantine is strong, but your images within the poem are all fluid.  There needs to be a connection between the hard spirit of resistance and overtopping the mark - which triggers it.