In a whole bunch of myths, Zeus is the one up to no good. Like the many corrupt politicians to follow, Zeus spends about half of his time seducing innocent young maidens and the other half trying unsuccessfully to hide his affairs from his fuming wife Hera. In the tale of Tantalus, however, Zeus actually comes out as the good guy.
When Tantalus commits his horrible crime, Zeus acts as a force of justice. Not only does he punish Tantalus, but he also rights the wrongs committed by putting Pelops back together again. Quite often, Zeus was worshipped as a force of justice in the universe, as the guy who made sure that everything was fair and right. In this myth, we can totally see why.