> Euros have also swung around by 15-20% over the past 2-3 years.

In relation to the dollar. Which is totally irrelevant for day to day transactions inside the Euro zone. I still pay the same price for a coffee I did 2-3 years ago.

But at the moment Bitcoin volatility is still huge: It's currently not reasonable to offer coffee for a fixed number of Bitcoins, that, say, stay stable over a year.

Your analogy between debit cards and Bitcoins seems a bit flawed too: For the purposes of international transfers it might be apt, but for small day to day business like buying coffee, it may be better to compare it to cash. And then there's no bank stopping you from transacting in cash.