[cowtools]

>you will always reach an equilibrium point where it will be profitable.

That is my point- that equilibrium point will eventually be low enough that 51% attacks, selfish mining attacks, etc. become feasible and highly desirable to execute.

>It's low reward, extremely high cost

It is currently low reward/high cost. But it will eventually not be.

>and 'easily' undone if the market so agrees.

False. Bitcoin has not made a hard fork in how many years? Can you make a hard fork faster than the attacker can "cash out" to crypto-crypto exchanges? Highly doubtful.

>Whoever mines the block will get no coins, but will get all revenue from the fees attached to whichever transactions are processed.

... which is dependent only on the fee market, and currently amounts to a small fraction of total block reward.