Bitcoin has a lot of interesting failure modes if the price falls too far. People will start taking mining hardware offline. This will result in a lot of idle

Bitcoin has a lot of interesting failure modes if the price falls too far. People will start taking mining hardware offline. This will result in a lot of idle capacity. There will be a number of people capable of pulling off a 51% attack. And if the hash rate falls very quickly, say 50% in a week, the difficulty adjustment will be unable to keep up. This would have all sorts of nasty effects. If the price goes to $4000 it should go to zero. That's assuming that the "investors" will behave sensibly, which is never a safe bet.