[tesco samoa]

Mongolian society from the 300's to the 1500's believed in plundering there fallen foe's Taking what they conquered as theirs.

In that society that was what was right.

If we lived in a society where we had to give up our first born to sacifice then that would be right. Those who hid their first born would be wrong. As per that societies laws and customs.

To answer your question. If the majority of people stated to kill their neighbours in your society right now. It would be wrong according to the laws and customs of your society. But if the trend continued within your country I am sure that some of the laws and customs would change to reflect this change in society. So then it would not be morally wrong according to that society. Remeber 50 years ago in your country it was morally wrong for a black person to sit in the front of a bus. It was morally wrong for an Irish person to apply to many jobs in the Toronto area.
But luckly society changed and the laws changed to reflect these changes in society. Which drives the morals of a society. It is based on the laws and customs of that society at that time.