Why it’s impossible for normal people to prove anything to Muslims?

It’s quite simple. Normal people think that something is good if it makes you a good person, and that there’s an objective frame of reference for “good”, in a sense that it’s intuitively clear that some things are evil, and it’s perfectly understandable for God to expect people to do good and refrain from evil, and if they don’t, they will be punished.

The Muslims, however, utterly lack such a frame of reference. They think that something is good if Allah commands it, and it’s evil if Allah forbids it. If Allah commands you to help someone, it’s good. If Allah commands you to kill that same person, it’s good. Basically, there is no morality outside of Allah’s will, as expressed in his commandments.

So basically, if you tell a Muslim that Islam is wrong because it makes people evil, he’ll look at you as if you said two and two are five. Not only will he not be convinced, he won’t even understand what you’re talking about. Islam is teaching the Muslims to obey the will of Allah. If the will of Allah is correctly written by the prophet, and it hasn’t been corrupted in the process of transmission, and one obeys it, there’s nothing better than that, because Allah completely arbitrariliy defines what’s good or evil, and all you need to know is that there’s no God but Allah, and that you submit to his commandments. The result is the only good there is.

Essentially, an ideal Muslim has the mentality of Adolf Eichmann. If Führer ordered him to help the Jews, he’d be known as the greatest benefactor. If Führer ordered him to calculate prime numbers, he’d calculate prime numbers. Since Führer ordered him to exterminate the Jews, he did that diligently, and he simply saw nothing wrong with it, because the Führer decides what is right or wrong for him to do, and it’s not for him to question, but to do as ordered, to the best of his abilities.

Or, as I put it once, never trust the hygiene of someone whose religion prescribes cleanliness.