Hi,
Let's take one thing out of the way: I don't support any of the dictators you mentioned and I don't support colonialism and capitalist excesses. It's the same as I hope you don't support any of the Muslim bloody rulers, invaders, and dictators throughout history, starting from Muhammad, as well as I hope you don't support Arab slave trade, etc. I wrote about those things simply to show that it’s unfair to blame only secular societies for everything bad that ever happened — religious societies were no better. We are all humans. All our societies in history did bad things. So let's not play the blame game.
And yes, as I wrote before, I believe there are ethical rules that do not rely on any god's whim. We don't know them exactly, but as a society, we can progress towards a better approximation of them. I believe this progress, as faulty as it is because we are only human, is a much better and more objective solution than any other option we have. This is not arrogance. This is a well-established idea in secular philosophy. It would be better if you take it seriously.
Your response that I'm arrogant and God is so much greater, and how dare I, and so on, shows clearly a difference between us. Your defense of God's rights to do as he pleases is - in my eyes - really a surrender. You admit that God is like Sauron in the Lord of the Rings. You admit that in the end you do things this or that way simply out of fear of him. Fear of being tortured forever otherwise. And maybe somewhere there is also a small carrot of that if you do things the way he wants, then you will get a reward when you die. You will get wine, and food, and sex slaves... To be honest, even this idea of paradise seems very low to me. And cringy. But, come on, of course not being tortured forever is already a reward. Paradise is redundant.
What you refer to as God's justice is not justice at all. It's a very basic human desire for revenge. We want to exact that revenge on our wrong-doers and when we can't then, well, who can?... "Maybe God... And what that revenge could be?... How about the cruelest thing we can imagine... how about eternal torture". See, this is all human imagination at work. Even if I believed in God, I don't think God would be like that. It's cruel and unnecessary. It's evil.
In secular ethics, we seek to understand reasons for doing things without an appeal to authority. Good things should be good by themselves, not because someone told us they are good. Bad things - we should avoid them because they are bad in themselves, not because we fear punishment. We try to do good and avoid bad because this is what a good person would do (here I present a somehow simplified view of virtue ethics, one of the schools of thought in secular ethics; there are others, but you should get a general idea). We seek guidance in texts and speeches of philosophers and other people we hold in high regard, but they are only there to help us. We discuss with each other, we try to foresee the consequences of our actions to the best of our abilities, and we try to fix our previous errors. In fact, I find it not only not arrogant, but much more humble than if I was to do something because God commands it and then never admit I did something wrong even in presence of growing evidence of my errors.
Same thing with justice. Justice should not be about revenge but about making the world a bit better. As a society, we discuss different options and try to find out how to fix the injustice, but we definitely don’t want to jut make the criminal suffer. You wrote about a murderer and asked about capital punishment. I'm not a fan of capital punishment. I think there are better options and I explained them before. But even if that murderer was executed, it would still be much more humane, than eternal torture in hell. The eternal suffering of a criminal does not serve any purpose other than revenge.
So, I hope that explains my position. If you look for something better than Islam, here it is. Humanism. Secularism. Believing in people.