SPOILER
The moral, I thought, was that money corrupts everyone and makes them do terrible, desperate things. As did Simone.
Also, the Sirens in Greek myth were beautiful women with the heads of birds who ensnared and trapped men. I found it clever how they turned it around and showed us the duplicity and self pity of men by the end. Plus how Kiki was reviled as a monster, because she was a beautiful and powerful woman, but the real monster was Peter, dressed up as a nice man.
Not meant to be modern or progressive; just realistic and dark, I thought.
I did think Peter swapping wives on the turn of a dime could have been better handled.