Tooth Fairy Bullshit

[GUBU]

That's some ludicrously obvious bullshit right there.

He's  right though. On what basis do we claim that a particular act is objectively good?

Bolding mine.

We don't, we understand that morality is a subjective and fluid notion, and we behave with that in mind. Everybody does if they deigned to think about it. But monotheistic religions have seen an angle to use in pretending that morality is an absolute and unchanging value*, because it gives them a gap where they can insert their god, even though the gape doesn't exist in reality.

An example would be the modern idea of "presumption of innocence", an idea which is actually far more ancient than most think, having its earliest known expression in the Law Code of Hammurabi. But it fell out of favour around the time of the Persian empire and has only been readopted in modern times. At all times the attitude to the accused in a court of law was considered moral and just. Human morality went backwards in this case before rediscovering an earlier peak, readopting it and building on it (albeit imperfectly).

*As an aside polytheistic religions have a far better understanding of morality, allowing it to be subjective and fluid, mainly because their gods are allowed to be bastards, and are allowd to be evil. When monotheistc gods are depicted with the same attitudes, they either are depicted as goodness or a righteous punishment of the wicked.