The divine theory is only rejected my secularists and this not to say they somehow found the proof for God's lack of existence. It just a philosophical theory that holds no more weight than the theists belief in God.
As for secular laws being best, (communism works best for China, but you are against communism because of your one chain thought secularism. We don't need secularism because it's not fair at all. Secular laws have given women all the power in courts, men face harsher penalties for the same crime in secular laws. Any woman can now accuse men with rape without due process under secularism. I can go on and O. We don't have that confusion in Islam.
Firstly, you're misunderstanding the dilemma it is not about refuting existence, but refuting that theist morality is good morality in of itself. The argument isn't that God doesn't exist, the argument is that theist morality is not good and better alternatives exist.
In other words killing apostates/homosexual ect are only good because Muhammed/God said so, and this leaves the theist little room to argue for their world view.
Then you can discuss the basis for a belief in particular islamic God, that is omnipotent, omnisceince and personal and find little prove to support it.
Secondly, secularism is a first step but it cannot stand alone obiviously, the second part is a respect for individual rights otherwise you'll have China which is another form fo cruelty.
Many of the reason that men face harsh penalties and women are awarded is due to the biases we have from patrichal structures, where women are naturally and socially seen as better parents and less criminal though stastics support the latter claim.
Furthermore any women cannot accuse men without due process, the problem is not over-reporting og sexual harrasement/rape, it is underreporting, you creating an alternative reality.
Lastly those problems pale in comparison to islam, where free speech does not exist, government suppress whole people and women are abused at home at an alarming rate and face socital and governmental sanctions for reporting rape, see my article about Marituana as example.
This is highlighted by human index report, human rights watch, freedom index ect, the morality you represent does not yield better result in area of significance.