This is still a really fun and quick argument, even so. The risk might not be entirely "the Bitcoin market collapses in the next year" and the risk is an implicit perceived risk, so it might not map to reality. Those criticisms are valid. Nevertheless correcting for that you get something like “I can’t be more than 70% sure that Bitcoin is going to exist a year from now and I also can't be more than 70% sure that I can actually safeguard my bitcoins from hackers and/or malicious insiders, so combining those together as independent possibilities I can't be more than 50% sure that my investment will still exist in a year” with the belief being a belief-in-action, a ‘revealed preference.’
And the nice thing about any revealed-preference argument is that in some sense it’s also a thrown-down gauntlet. “Is this estimate full of crap, HN? Then put your eggs in this basket. Your fortune awaits.” Like, it’s not saying that your arguments are not valid to me, as if the Hacker News comment thread were some sort of arbitrator of truth if only we could argue loud and hard enough for our points of view. A revealed preference argument is saying that your arguments are not valid to you, in the sense that if you profess other confidences or values then your actions are not in line with your values. Who cares about the bluster on the HN comment thread then? This is something that you need to work out in your own case, wondering if you are convinced enough in the stability of Bitcoin to buy some Bitcoin right now to short the future, and if not then why not. Because if you do not have credit-card debt then that 24% APR should look mighty tempting.