Cote - I'm not sure what you mean. Other democratic countries manage to self-rule while in the Eurozone. The fiscal policy imposed upon Greece at the moment comes from not its Eurozone membership but its need to abide by creditors' rules if it wants more credit.
This is both true and not true. Perhaps it would be more accurate to say signing up for a common currency means, for those countries that do it, accepting significant limits on what an elected government is able to do without incurring problems that might have been avoided were it not for the common currency.
That is to say, a currency shared between different nations limits the sovereignty of those nations' elected governments, including the sovereign right to make stupid decisions on the electorate's behalf, and then live with the consequences. If you're on your own, with your own currency, that's your problem, you devalue and hopefully bounce back. If you can't devalue, as has been exhaustively discussed upthread, you're a bit more stuck and basically just shouldn't have got into the pickle in the first place. But because no-one wants people to start questioning the single currency, instead you get bailed out with endless loans, in exchange for accepting that other people are going to tell you how to run your tax and welfare systems.
I think what is complicating this crisis most is the fact that it is not just about economics: under the surface there are fundamental conflicts about the proper mode of government in a globalised society. Should we be aiming away from nation states towards an international technocratic, social-democratic supra-government based on universal human rights and consumer capitalism underpinned by taxation and a welfare state? After all that is what most of northern Europe has, with relatively minor variations. Or do nations still correspond to blocs of cultural and political identity such as to be a better vehicle for different peoples' management of their own interests?
The eurozone (and the EU generally) has muddled this question, because in order to function properly it requires a social-democratic supra-government etc, but has been implemented on top of multiple, divergent nations most of which still seem to believe that their elected governments are in charge. I would argue, though, that they are probably mistaken, and inasmuch as different countries still seem to self-rule, that this is mostly because their electorates haven't yet voted for anything that sets the democratic mandate of their national government fundamentally at odds with the interests of the supra-government.
I've been riveted to the Greek crisis because to my eye it's only superficially about economics: fundamentally it's about how and from where the nations of Europe are ruled.