Is the Slaughter Justified?

In Book 22 Odysseus with the aid of his son and loyal servants slaughters all the suitors (despite the pleas of mercy from some of them), all the maids, and even the priest Leodes. Are these killings justified? Could he have punished them without killing them? Could he have driven them from the house. Are some of the killings justified, but others not? What about the people they spared (Phemius and Medon) -- what was Telemachus' reasoning? Was it wise or prudent to kill them all?