In an Islamic state, there is no separation of church and state, so the Koran (and example of Mohammed as documented in the hadiths) is used as a substitute. It is immutable, of course. Apologists for Islam are likely to justify the extreme passages of the Koran by pointing out the the U.S. Constitution, as originally drafted, counts blacks as 3/5 of a person.
In response to that argument, I would suggest making the following offer:
If the apologist for Islam will stand up on a soap-box in front of 10,000 Muslims in an Islamic republic (Pakistan, Saudi Arabia, etc., take your pick) and shout out that the Koran is wrong and Mohammed was wrong to justify taking slaves, having sex with them, and killing non-believers and apostates and the Koran should be amended; I will stand up on a soapbox in front of 10,000 people in our Constitutional Republic (the U.S.A.) and shout out that our Founding Fathers were wrong to count blacks as 3/5ths of a person and that the U.S. Constitution was rightly amended to delete that onerous provision.
What will happen, of course, is that the apologist for Islam will avoid taking up such a challenge, knowing full well that he would be put to death for apostasy in the Islamic republic; while a person in our constitutional republic making an assertion that our Founding Fathers and their central document were in error would be met with yawns, and an explanation that even Frederick Douglass knew made both the document and the nation a righteous endeavor, an endeavor in teh service of freedom, liberty and justice for all. The Koran, not so much.