I personally don't have a problem with the fact that you allowed the fish to die. You essentially did what breeders do - you selected the best and culled the rest. I myself have mixed gender platies but I rarely even see a fry because they are being eaten by the other fish in my tank. It's just that your logic is very strange... "I don't want to give them to someone else who might mistreat them. So instead I'll let freeze them to death".