I guess the normal way. Biologically there might not be anything wrong them.
Socio- Cultural norms in harder to reach geographies are formative for such a thought process. What might seem heinous to you and me might seem perfectly acceptable to a large section of people. Polygamous relations are an anathema in many societies but perfectly acceptable in others. Child labor which will make westerners queasy is considered socially acceptable and economically necessary in countries like India.
Good and Evil, Crime and Punishment and other moral theories are a product of societal constructs and no less arbitrary and as horrifying it might sound, it says something about we as a society when we don't blink when thousands die in Govt led pogroms but a mutually acceptable societal constructs like Jirga or Punchayat (which I might add only have legitimacy due to failings of govt systems) are criticised for imposing the democratic (in the truest sense) will of people.
@Joe Shearer @Solomon2 @Oscar