Genuinely curious; would you say the same about an increase in supply from 21 million to some extended schedule of emissions to secure mining? I'm guessing you would. I do find it interesting that bitcoin could ultimately be 'hoist by its own petard' in this sense. Satoshi's 'set in stone' idea was that fully permissionless *evolution of state* of a fixed protocol is possible, using large scale proof of work. But that 'fixedness' is ofc just human consensus, and if the proof of work moves to a less ... stone-y system, the security is lost.

Absolutely. It's impossible to create a protocol that is absolutely impossible to change: the best you can do is to align incentives that make certain aspects unlikely to gain sufficient consensus to coordinate a change. With regard to changes in the absolute / effective money supply, the only way one could imagine gathering consensus to change them is if it's done to avoid some sort of catastrophe.