About hoarding coins and never spending them while the issuance of new coins deflate?

It's an open protocol, we can see whether old coin are being spent (and they are). And to Toxic Positivity's point about millionaires just sitting on them, I would expect they will spend them if they come to realize that it will lose all it's value, otherwise it's a lose-lose situation for them. If they don't then there is even less supply than 21 million which will increase the value of coinsacrually in circulation, if there's demand for it. We already have pretty solid reason to believe a few million Bitcoin are gone forever, so available supply is less already.

I totally get the skepticism, especially when Bitcoiners act like there's no possible way Bitcoin could fail. It could totally fail, but it's a really well designed system of incentives.