Morality is a human created thing.
It's been a long time since I've posted here. Just got bored and thought I'd post back.
Anyways here's my take.
Things that are artificial are also by default open ended because humans could have made them however they wanted to. Differences in morality is no different from differences in metric and the english system.
On the other hand, if morality is derived from human nature: say humans are naturally (through evolution) selfish though inclined to help others as long as it does not harm theirself, then all people would agree that it is moral to help others. This is an example of closed morality.