A currency with no mechanism for monetary policy is not going to be adopted. Bitcoin is purely deflationary for more reasons than just people losing their keys. For example, a fixed reward split between a growing group of miners will also cause a rising price floor. The miners will not sell for less than their electricity costs, which makes the smaller piece of the block reward they receive have a higher price. So yo…
It is not the deflationary policy that makes bitcoin less adoptable: being deflationary predictably is better than unpredictably inflationary. Specially in this day and age, where bitcoin prices can be tracked to the second and prices changed accordingly across the board. Its interesting to see there's research talking about how the ability to price things faster has changed the effect of monetary policy on prices at all.
The rest, I agree. It has a very speculative value, and its best usecase is pass-through. But pass through is still a good use-case. Argentina, 3 years ago, would pay up to 5% of funds to transfer money in-out of the country: bitcoin would have been easier and cheaper. And its still used as a way to evade controls. The use of bitcoin can severely reduce the government's capacity to levy taxes, as it is way harder to track down than bank/card transfers. Whether that's moral or good will be secondary to the fact that it can do that. If its use case is to sell drug money and reduce taxes, it will have value.