Mother and son in New Mexico face jail time for incestuous relationship

[Excited Penguin]

They're not moral by my standards, they're moral by that society's however. 

I trust you understand now the sense in which I use that adjective at the moment.

Your problem is that morality is inherently personal, being both subjective and relative. Social morality gives rise to obvious contradictions which indict its usefulness in human life.

In Saudi Arabia, you'd be beheaded for your atheism, legally. Is that moral? Why or why not?

I'll leave you to work out the ramifications on your own. I don't think you've thought this through.

Morality can also be objective, as at a societal level. Laws are an expression of that kind of morality.

It is moral. It is moral for those who agree with it. As for why, I'll refer you to a definition of the word moral:

concerned with or derived from the code of interpersonal behavior that is considered right or acceptable in a particular society.