I go along with Researcher and "power corrupts." I'd also say that the absolute net is, "Crime doesn't pay." Michael lost everything by the end of the Trilogy.

Ntra la porta tua lu sangu � sparsu,
E nun me mporta si ce muoru accisu...
E s'iddu muoru e vaju mparadisu
Si nun ce truovo a ttia, mancu ce trasu.