
I personally don't see having a baseline for morality as evidence of god or any kind of 'rule book'. I see morality as another thing which evolves.
As an example, only 60 years ago Rosa Parks (I think) was arrested in the USA for refusing to give up her seat to a white person on a bus. Perfectly morally acceptable to most people then. Nowadays, hopefully, very few would accept this.
Racism is one of many moral issues mankind has fought over, we still have a long way to go in my opinion but what I consider to be 'right' seems to be winning.
Humans have evolved complex social structures and relationships no other creature on earth has managed, this is why we no longer live within the constraints of natural selection, learned morality in many ways is the reason for that. We no longer have to be the strongest to survive, in fact we actively look after the weak and the sick. This is how we evolve now, not physically but socially. Only in the psychopathic worlds of multinational corporation management or politics do we still see the weak destroyed for personal gain!
To take your point about Hitler, if he'd had his way and created his version of the world, would his morality become accepted? Possibly, but I don't think so. For one, his view of the world was impossible to maintain and would inevitably self-destruct, as most dictatorships have done throughout the ages.
However hard they try to destroy it, kindness and understanding and all that hippie sh*t will prevail. Not because god makes it so, but because we are human and we've evolved to enjoy being nice to each other. The only way humankind can continue to flourish is by being nice, simple really!