You could also reasonably argue that the US is a perfect example of what the OP thinks is impossible. The primary differences are that we have a far more mobile workforce than does Europe, we have effective caps on state debt levels, and we have a (much hated) unified tax system that allows federal tax money to be spent in states that are lagging economically. Despite conservative hatred of these latter two items, they have done a lot to keep us from going through Greek debt crises of our own.