It's a fair point but it means they are not part of the Euro financial system and would not have the oversight, lending rates, financial integration etc. etc..

It's a fair point but it means they are not part of the Euro financial system and would not have the oversight, lending rates, financial integration etc. etc.. And they have the option to leave at any time. Case and point: nobody is strongly complaining about getting Kroners for travel etc.. Imagine if every nation did with Denmark did - and made small adjustments - then you'd have 'currency harmonization'. So I think you have a fair point but still, Denmark is not Euro.