Given this possibility of simple exit from any and all of the European tax systems (and such exit does not require that one stays in the EU either) the theoretical peak of the Laffer Curve is lower in Europe than it is in the US. Where such exit is very much more difficult.
From the perspective of Brussels and Berlin, maddening though Athens may be, there is no alternative but to double down on Greece -- because a Greek exit would have huge ripple effects through all the Mediterranean economies (and their banking systems).