What does Islam command a Muslim to do regarding atheists who debate merely for the sake of arguing, not to reach the truth, and what is the proper response to atheists' accusation that a Muslim says what he does not understand when he conveys fatwas and articles in his discussion with them?

The atheist's claim that the polytheists asked the Prophet to ascend to heaven and he did so is a false claim. This is because Allah did not fulfill what the polytheists requested from His Prophet. The polytheists' request was that they see the Prophet ascend into the sky before their eyes and bring down a book for each of them. This did not happen in the Isra and Mi'raj, as none of the polytheists saw the Prophet ascending. Rather, they disbelieved him, and some apostatized from Islam when he informed them of the journey. Some scholars even held that the Isra was a spiritual experience or a dream.

The polytheists only made that request out of stubbornness. Had they desired the truth, they would have been answered. However, Allah opened the door of repentance and mercy for them instead of punishment.