If he's like the mafiosi back in Italy then I reckon it is simply as you stated, because his family were wiped out and like any down to heart Italian mafioso would definitely want to get back at the people responsible.

The Americans don't even kill rats anymore, I mean I really think although it may benefit them in the long run, it does set a bad example. In Italy you wouldn't hear of any mafia letting something like that happen and just forget about it.