This is nothing to with fairness. Greece need debt relief or it will collapse, and the creditors will still lose out. You're no doubt familiar with the concept of drawing a line in the sand and making decisions for the future common good, as happened with Germany's debts after WW2.

The potential long term political and financial cost of abandoning Greece far outstrip the 70B it owes Germany. It will leave the European project in tatters, despite what Merkel assures us.