I understand why German voters are unhappy with having to fork over more of their money. But I can also see why German leaders ultimately support the bailouts. It's not about the loans being repaid, since lenders have already lost a lot on their Greek holdings from haircuts and bond swaps. It's about stopping the contagion from a Greek default.
If that happens, it'll be game over for the Eurozone. Markets will either stop lending or make interest rates too expensive to afford. That'll force Spain and Italy to turn to the bailout funds for help, and it's those two that has everyone worried - they owe trillions
in external debt and there's no way any sovereign or mechanism can cover them.
Since it's unlikely they can be helped, Spain and Italy will default and things start unravelling from that point. Less capital being available stops lending activity, which can only mean more defaults and therefore the disintegration of the Eurozone. And this is where Germany's probably most concerned. The single currency makes German goods affordable; without that advantage Germany wouldn't have the level of revenue and surpluses its been getting from its exports.
And because Germany depends a lot on its exports, a slowdown in those industries would be especially tough. If the DM were to be re-introduced, Germany goods would become more expensive because of the higher exchange costs from the currency appreciating. Revenue from exports drop and that's where the freefall would start: businesses stop investing because no one will buy their goods; employers can't afford to pay bills or keep their staff; government finances become strained from getting less taxes while having to dish out more welfare support, etc., etc.
So I reckon from the politicians' perspective, the bailout is probably outweighed a great deal more by what the costs could be from the Greeks defaulting.