I hate Bitcoin as much as the next person but it's not really fair to criticise a technology that's potentially cool on the grounds that it doesn't have enough adoption. If it had the stability of entire countries behind it, it wouldn't fluctuate this much and even if it did, if everything's in that currency then you don't notice it in daily life either.

The problem I have with it, is that the technology is inefficient at solving the problem as compared to a central authority issuing currency. Something using e.g. blind signatures sounds really cool but the tech was ahead of its time (paper stems from 1983) and by now it doesn't sound cool and new anymore. Example implementation: https://en.m.wikipedia.org/wiki/Ecash

> it's not really fair to criticise a technology that's potentially cool on the grounds that it doesn't have enough adoption

But that's not at all why the person you're responding to criticized it!

> If it had the stability of entire countries behind it, it wouldn't fluctuate this much and even if it did, if everything's in that currency then you don't notice it in daily life either.

Common misconception. You basically need currencies tied to countries (more precisely, OCAs or optimal currency areas, characterised by either 1. homogeneity with respect to external shocks (not the case e.g. within Europe), 2. complete factor mobility (not the case e.g. within Europe), or 3. transfer payments (that is, fiscal support)).

In other words: If there were one currency (only), even with the stability of entire countries behind it, it would still fluctuate too much to be very useful. Or, to put it different again: You need FX. One currency is not enough.