This. Ultimately the defence blockchain has against hard forks is exactly the same as the defence other monetary systems have against things like hyperinflation

This. Ultimately the defence blockchain has against hard forks is exactly the same as the defence other monetary systems have against things like hyperinflation and mass asset seizure which cryptoenthusiasts worry about: generally the people with the [hash]power have strong incentives not to do so. Except when those incentives change. In both cases, how much confidence you can place in that theoretical incentive structure protecting you varies widely according to who and why (you can be pretty confident that your US dollars won't be hyperinflated, the contents of your Swiss bank account won't be seized to balance another government's books and nobody with significant hashpower cares that you scammed Joe Sixpack out of BTC. You can't be so confident your Venezuelan Bolivars or shitcoins won't become worthless next month or that you'll get to spend gains from a heist against an Ethereum Foundation or US government flagship project.