In a Vox column, Thomas Philippon suggests a 3% rather than 4.5% primary surplus target on fairness grounds. His central points are:

Greece ran a reckless fiscal policy during the boom years, wasting much of the money that it received. There is no question that Greece needs a strong dose of fiscal consolidation. However, Greece’s debt should have been restructured much earlier. This restructuring was prevented by legitimate fears of contagion, and it is not fair to ask Greece to pay for that delay, which reflected a general lack of preparedness among Eurozone policymakers.

Philippon’s estimate is similar to another estimate by Paolo Manasse.