Which rather proves my point - that they are adhering to an absolute moral authority.
You seem to have missed the point - it does not matter whether there is an absolute moral authority existing somewhere if we acknowledge that as humans not only are we are fallible in our interpretation of morals, but that there could be multiple interpretations that could all be acceptable or not and we would never know which ones are acceptable and which ones aren't.
This puts us in the same reasoning position as people who are reasoning morals without referencing what a god may or may not think about any issue. We form views based on the imperfect information we do have available to us and we will never know what the correct moral position is in any given scenario.
Within secular moral philosophy you won't find the equivalent - in other word some appeal to "Kant knows best" or "Bentham knows best" etc.
No but since the saying "Allah knows best" is used as an acknowledgement of human moral, emotional and intellectual imperfection, it would be a bit odd to claim any human knows best.
While some may not be sure their interpretations are correct, what you are saying is that they think that there is a correct interpretation which becomes beyond challenge, as it is the divine authority of god.
Nope - what I am saying is there could be multiple different "correct" interpretations in any given situation and it is not for humans to insist that their particular interpretation is the correct one.
Now I don't know that many moderate muslims to the extent that I am able to discuss such matters (that said I know and work with many, many moderate muslims, but they are professional colleagues so this type of conversation tends not to come up). However I do know plenty of moderate christians, and while these people tend not to be tub-thumping absolutist bible-literalists, there are certainly elements of 'accepted' moral truth which isn't really questioned even though they might claim that "Jesus knows best".
Um there seem to be a few tub-thumping atheists on here who try to give the impression that their morality is an 'accepted' moral truth. People's style of communication can come across as absolutist - it depends on their personality
https://www.psychologyjunkie.com/2019/08/17/heres-your-arguing-style-based-on-your-personality-type/And of course the issue isn't with the moderate, but the extremist - the person who not only considers that there is a correct interpretation which becomes beyond challenge, but have absolute faith in what that interpretation is and that it is murderous. That is where the whole notion of there being a moral position that is the divine authority of god becomes deeply problematic. As soon as you buy into that notion you have lost any meaningful argument with someone who interprets what that devine moral authority thinks as different to you but believes it with absolute and unshakable faith. In their minds they are following diving purpose and obligation, just as you and other moderate muslims think you are following diving purpose and obligation. But what that leads you to do is massively different.
Sounds like the problem is people having an absolute unshakable belief that what they think is right. I and the moderate Muslims I know don't think we are following divine purpose and obligation, but we do think we are trying to follow our interpretations of religious traditions that have been transmitted through the centuries by oral tradition from a man in 7th century Arabia and therefore our interpretation could be in error.