> If money is easy to debase then it will get debased a lot in the long term.

What happens to money in the long term doesn't matter much, what happens in the short term does. Investment vehicles short-term fluctuation matters less, but their long-term performance matters more.

> That leads to inefficiencies in the market, and in particular to less sustainable behaviour of people and less sustainable societies.

I see no reason to believe that the long-term smooth decline in the value of money does that at all compared to achievable alternative behaviors of money. In fact, one of the reasons money is typically managed with a goal of low-but-positive inflation with low volatility is that there is quite a lot of experience suggesting the opposite.

Economies need a human-in-the-loop to adjust the settings every once in a while. That's what monetary policy does - it changes the money supply and interest rates as a response to what happens in the economy. Thinking that you can lock that policy in place once and let it run forever is naive - it just doesn't work in practice. This is why we don't have the gold standard anymore - it was a system so bad that it eventually broke and we had to move away from it. That's where all the talk about sound money ends - money has to be "unsound" in order to work in the real world.