Yeah that is the interpretation of that particular story I got too. That the real sin was being inhospitable to guests. But I got the impression it was a commentary on generalized hospitality towards people. Of course the failing in the story is the implication you made that it is better to give them your own family than to let them harm a guest in your house. Although I doubt the Bible actually intended to advocate that notion. I really think the basic moral of the story is "treat strangers better than you'd treat your own." That is not to say it is ok or suggested you treat your own worse mind you.