The forex example is a bit off, though. If I don't believe the price of the Euro, for example, well, there's still a ton of stuff being produced in countries that use the Euro, and they trade with other countries, and that sets a price for the Euro in relation to those other countries. But how much stuff is produced in places that use Bitcoin?
Perhaps I should have said in "places" that use Bitcoin, because it doesn't have to be countries. But how much stuff is for sale only in Bitcoin? That's where Bitcoin is going to have a price as a currency. If there aren't many things with Bitcoin-only prices, then Bitcoin can still have a value, but it's value is more like gold - as an investment that's not subject to inflation. Even as that, it can have a value forever - gold's done pretty well at that, after all.
But I still think it's too soon to see if Bitcoin will do that. Gold has several millenia of being accepted; Bitcoin has 10 years. We'll see what happens in the long term.
Objection, your honor. Assumes facts not in evidence.
We get it, you've bought in to the idea that Bitcoin is the one true currency. (That's why a statement like "1 Bitcoin is still 1 Bitcoin even after 100 years" makes sense to you.) The rest of us, however, are not sold on this. We suspect that 100 years from now one Bitcoin will get you exactly nothing of value. Speaking to us from a perspective that Bitcoin is the one true currency is completely unpersuasive to us. If you want to convince us, you need to tell us something that makes sense in our viewpoint.
> Take any point in Bitcoin's history and compare its value then to three years earlier. There is no case where it was worth more three years before.
That's a decent attempt at doing what I asked for. Unfortunately, I find it less than persuasive. It's an asset that has a total history of 10 years; there's a pretty small sample size here.