It seems we do part company. But I do have one request. If you cannot believe, let alone defend based on your worldview, that some things are simply right and others wrong, for all individuals and cultures, at least stop claiming you can explain morality without the supernatural.
As for those moral precepts which are common to all cultures, if there are any, they are determined by observation and comparison...and there origin is most likely to be found in genetics.
To me your claims of morality originating in the supernatural are just so much superstition.