Yes, there is a level at which it doesn't make sense any more. In a sufficiently efficient market, that is the point we are at, at any given point in time.
I believe the bitcoin mining market is efficient enough already that we're more or less there.
That shows the primary failings of putting all trust in an efficient market. The "makes sense" breaking point in an efficient market is when it stops making financial sense for the miners. It relies on rational miners who don't don't succumb to the sunk cost fallacy after investing large sums upfront in mining rigs. While it also ignores the negative externalities involved in increasing global electricity usage like climate change.
Yeah, I hadn't really considered how simple economics essentially forces this to grow to exactly the point where the externalities are unsupportable based on the benefit provided.
