Here’s Tim Worstall concisely explaining why the euro is such an ill-begotten beasty:
The effects of changes in interest rates will be hugely different in places where the vast majority of housing is owner occupied (UK and Ireland) as opposed to rented (Germany, say). And hugely different where mortgages are floating rate (UK and Eire) as opposed to fixed rate (Germany).
In the former a lowering of interest rates reduces housing costs for almost everyone. In the latter it only changes costs for the marginal uptake of new housing purchases. Similarly, a rise in rates will lead to a huge reduction in spending power in the former model while having little effect in the latter. So whether it’s boom or bust, the effects are greatly magnified in one type of economy: something of a problem when those rates are being set for the other type of economy.
Right back from the late 80s this was obvious. As it happened, it turned out to be the low interest rates needed by the euro core countries that screwed over Ireland (aided, yes, but not caused by, the local corruption and banking stupidity). But if it had worked the other way around, if Germany and France had been facing inflation and thus interest rates were set to reduce that, then Ireland would still have been screwed over. Just the other way: whether you’re getting screwed missionary or doggy style you’re still getting screwed.
Single currencies in non-optimal currency areas just don’t work. Period.