Theological morality is not based on things like culture and science, which change all the time. Instead it’s based on divine words of God (Holy Books), and acts and words of prophets who are constantly checked and corrected by God to always act good. In Christianity and Judaism other people also have a say on morality, but in Islam morality completely originates from God, goodness is obedience to God and badness is disobedience to Him. In fact, all moralities except those which are based upon an ontologically higher and omniscient entity like God are subjective and non-normative, since they all rely on products of human mind, which always change (science, culture, etc.). Why should I be prosecuted for theft or murder? Just because you feel so? Countless other people in history felt otherwise. Even if all of humanity feels I should be prosecuted for a crime, I will ask, what makes mere feelings normative? It doesn’t make any sense at all.

I think we should be better than “We can’t see anything objective to base our morality upon, so we’ll just base it upon our feelings.” mindset. We should be able to at least admit we don’t have a normative morality and our laws and law enforcement is simply bullying people and making them submit our (collective) feelings and desires because we have the power and means to do so.

Regarding the question what God says being subjective: No, there are arguments of current and past miracles, and recorded honesty, reliability and mental health of prophets, and many other things. At least for Islam. You can search. If you have questions, simply refer to this playlist [1]. Every question regarding Islam and modernity is (repeatedly) asked there.

I could write a lot more but I have a lot of things to do so I’ll simply direct you to this documentary series [2] which elaborates on morality among other things. Both playlists are intellectual gems no matter what your background is.

0: See Rabbis having authority and knowledge over God in Judaism, and countless versions of Bible which are clearly not all the exact words of God, and instead of non-prophet humans. Also Christianity and Judaism doesn’t see prophets as constantly checked and sinless. See examples of sins commited by prophets in Bible and Old Testament.

1: https://youtube.com/playlist?list=PLcnL9bB-q3ylQ9CZdB8YfjoDv...

2: https://youtube.com/playlist?list=PLcnL9bB-q3ymnRNcpZGcVVjiD...

The Holy Books where written with the morality of the time in mind. Which changed and thus people ignore parts of it.

I still don't understand how "guns in E.T." can be "the truth"

Muslims maintain they were not written, they came directly from God. Also, Qur’an radically changed many moral values of the society at the time (most significant one being changing the state of polytheism from worship to blasphemy), and Muslims faced very strong and violent opposition because of that. I don’t know the specific subject of guns in E.T, but Islamic morality covers every single subject in life without exception. I didn’t say they are truth, I say there is one truth regarding their morality: They are either good or bad.