No currency is guaranteed to be deflationary. You may guarantee that the currency supply will behave in a certain way (although even that is debatable), buy you cannot guarantee that the price level in terms of such a currency will continuously fall.

The fixed currency supply guarantees it: unless the economy is shrinking at the same rate, each BTC becomes more valuable over time and that’d cause purchase prices for goods to trend lower.

This has been a key part of the sales pitch for a decade: buy now and it’ll be worth more later, guaranteed, but that’s not good for an economy since it heavily incentivizes holding onto anything you aren’t forced to spend. Since Bitcoin has no innate demand, that’s an especially dangerous cycle since almost everyone has alternatives.

> The fixed currency supply guarantees it

No, it doesn't. Bitcoin can lose 50% of its value in a matter of hours, as recent experience shows, despite being in a limited supply.

So the only way bitcoin isn't deflationary is if demand for it continually goes down over time until it's irrelevant. If demand either goes up or stays the same, it will behave deflationary (wallets getting lost). This doesn't seem to be a good performance pattern for a currency.

You're right a fixed supply isn't enough to guarantee it, you still need productivity growth and technological progress, something we've had for a long time. Given enough growth a 50% crash is nothing.

There isn't monetary deflation in bitcoin (expect for lost coins).

As a global reserve currency, bitcoin would act as an "index fund of everything". Economy is expected to grow, but it's not guaranteed. Which means that there's always a non-zero risk associated to it. There's more risk on short time scales, and less risk on long time scales.

There will be if it's successful - 90% of the bitcoins ever mined have already been mined, for bitcoin to be useful at a long term world wide level it needs to store enough value even as the size of the world economy grows - if it can't them it will become a limit on economic growth much as gold became in the last century.

So because the number of bitcoin is fixed to remain relevant bitcoin will need to continually deflate (ie increase in value) so that there's enough to represent the size of the economy

>More importantly, the people hawking it _really_ want it to be deflationary because that effectively makes them landed gentry getting richer without any effort on their part.

Yeah it is basically people getting screwed by increased wealth inequality and then as a response they don't think of a way to build a system without losers, instead they join a system where the old dynamic makes them the winners. The only difference is that you start from a clean slate from 2008 onwards.

> as a response they don't think of a way to build a system without losers

Which system is that?