Since mentions of ancient times (the Crusades), genocide dangers and shady political motivations have been made, shall we talk a bit about the political effects of Islam and genocide?
Islam is about 1400 years old (or far older, according to its own doctrine). It has been wildly succesfull in the demographic sense, to the point that even today one in every four people in the world is at least nominally Muslim.
A large number of countries explicitly claim Islamic inspiration for its policies. Even so, it is quite the challenge to have people agree on whether any given country can be called Islamic. Apparently Saudi Arabia is not accepted by many as an example of an Islamic country. Neither are Turkey or Iran. Not sure about Egypt, Lebanon, Iraq, Kuwait, Syria and others.
A Caliph is generally understood to be in some sense the current day successor of the Prophet Muhammad as leader of the whole Islamic World. Both ISIS/Daesh and the Ahmadiyya Muslims presently make claims at being a current day Caliphate. Most Muslims reject both, which is not to imply that there is not much longing for a Caliphate.
That is nothing new. There were several parallel Caliphates in the past as well. The first Caliph dates back to 632 and until 1924 there has hardly been any time without a Caliphate except perhaps for 1258-1261. Shia and Sunni views on the matter seem to diverge somewhat.
The latest widely accepted Caliphate was the Ottoman Caliphate (1517-1924). It lasted over four centuries and for much of that time had at least nominal rule over large territories in Africa, most notably what is currently Egypt and Sudan, with litoranean reachs spreading well into the West and South/East. It also controlled most of what is currently known as the Middle East.
It also had a long, painful decadence. Its last few years were remarkable for its somewhat puzzling involvement in World War I and for the rarely mentioned and rarely acknowledged genocide of the Armenian people out of political convenience.
So it is not like Islam has never been given a chance to show its wonderful results as the source of political wisdom. Quite on the contrary, it has been tried pretty much non-stop for centuries and the results have consistently been abysmal. Blaming that on "Islam's enemies", most often nicknamed "the Crusaders" these days, is a common but very unconvincing claim. It is the creating of a phantom escapegoat to take the blame for the failure of what is supposed to be a God-protected wonder. The actual results fell under their own weight and caused a lot of bloodshed and overall decadence. Time and again, consistently, for centuries. These days the Islamic World does not even have any vestige of the dearly remembered accademic prowess that it was once famous for.
Why should anyone feel compelled to give Islamic policies, including Sharia, the benefit of the doubt yet once again? Particularly once it is acknowledged that there is explicitly no intention of reciprocity there? Islamic groups rarely even pretend to make claims of being willing to rotate the political power they seek with secular or even Christian movements, for instance. Because that would be betraying God's Will, presumably.
While the presentation is confused, misleading for various reasons and often sincere and well-meaning, the end result is still a situation where we are invited to please consider surrendering much of our personal freedoms and our destinies to God's Plan as revealed by the Qur'an. If most of us disagree, that is ok; they will just insist that the majority should decide the policies and take some confort in their impressive birth rates, with a barely disguised expectation that we will eventually submit in some way or another.
Islam is a sobering warning for the dangers of taking theistic beliefs too seriously. What it is not is a succesful recipe for a healthy society, if the actual history is any indication.