It's mostly unstable up. Virtually anyone who holds Bitcoin over 1 year sees their savings not lose value, often with a good upshot, unlike _every_ currency in the world.
(1) BTC _always_ goes up. It did not annihilate after 4 giant bubbles with dramatic corrections. Only people with strong irrational denial who finally buy during the maximum frenzy have to wait a couple of years to return to black. Everyone else has to wait much shorter and then hold with a peace of mind.
(2) It is not harmful to people going long with their own money, but it is a huge risk to margin traders (both those going short and long, but on a loaned capital). But this is a positive thing because that's how you get the sound money bootstrapped: by incentivizing long-term holding and disincentivizing wild speculation.
> It is not harmful to people going long with their own money, but it is a huge risk to margin traders
Yes, appreciation on assets is great for owners.
But when talking about currencies (i.e. standard medium of exchange), it is the overwhelming consensus that deflation -- especially rapid deflation -- is harmful to an economy. The Great Depression being the most dramatic example of a deflationary spiral.
So you are saying, fractional reserve, paper money indistinguishable from IOUs and subsequent credit expansion blessed and coordinated at the federal level (with creation of the Fed) are totally not among the reasons that caused market distortion and subsequent collapse?
A far more realistic approach is to adopt another country's stable currency (e.g. US dollar).