> We will be at the whims of an algorithm that no one has any incentive to change.
Not only that. We will also be at the whims of a practically unchangeable algorithm that only works as long as (mostly) chinese mining operators keep their gigawatt-guzzling hashing machines running, and that has no suitable failure handling for the case of big parts of that hashing power suddenly going missing. Look up "chain death spiral" for a description of this specific doomsday scenario.
It really is intriguing to follow through on some of these scenarios in which Bitcoin sucks up enormous portions of worldwide economic power, only to catastrophically fail in one of the numerously envisioned ways in which it could fail. The higher the market cap rises, the more it seems possible that we are right now looking at the next worldwide financial crisis in its infancy.
Another thought: even assuming Bitcoin continues working normally and somehow being able to handle the transactions that come with a multi-trillion market cap, what about the fact that all this "value" is completely removed from the market where it would usually be mostly "at work" as operating capital of companies which in turn (not all of them, but in the grand scheme) generate actual value, as in improvements of the conditions for real humans? If this is not offset somehow, won't it cause a huge economic crisis of its own, possibly - in the worst case - leading to us (as humanity) not being able to keep up the stupid hashing game and thus making bitcoin entirely unusable and thus worthless?