Economic self-interest of states (and indeed individuals) is perfectly right and valid. The EU however has federal ambitions (don't forget that every German shares a common citizenship with the Southern Europeans, the first words on all our passports are 'European Union'), and the sight of Germany feeding off countries it's in economic and political union with is pretty outrageous. If European unity meant anything then *at the very least* there would be a system of fiscal transfers in place-you can't expect to continually take from the pot without putting anything back in it.
The bigger problem is that German economic policy is built around sacrificing Southern Europe in return for prosperity at home. The Euro is grossly undervalued compared to what the Deutsche Mark would have been, which gives German industry a big competitive advantage when exporting. But for countries like Greece, Spain, Italy etc it's grossly overvalued and that results in unemployment, low pay and stagnation. Germany needs those weaker states inside the club in order to keep the Euro relatively undervalued. Currency is the biggest economic adjustment mechanism there is, when you lose it then economic activity generally flows to the stronger regions (North/South divide in UK, North vs Mezzogiorno in Italy, etc). You can treat the symptoms primarily via fiscal transfers but Germany doesn't even want to do that, even when unemployment approached c.25-30% in several states.
