It is not a true statement to say, "Islam is a Monotheistic religion."
The true statement is to say, "Islam claims to be a Monotheistic religion."
There is all the difference in the world between these two claims.
"The Islamic concept of Allah’s unity teaches that he alone is to be served, that he alone is to be feared. Yet the Quran commands Muslims to fear others besides Allah such as the relationships established by the womb.
Although the Quran expressly says that persons are to slave only for Allah it also allows Muslims to own or be slaves, which means that they are not slaves to Allah alone.
Part of the service rendered to Allah alone includes bowing or prostration. Allah violates his own command of worshiping none but him by commanding creatures to bow or prostrate to other creatures.
The Quran says to invoke Allah alone, whereas other texts and references allow Muslims to invoke persons besides Allah such as Muhammad!
Related to this point is the express command of the Quran that Allah alone is a Muslim’s helper and intercessor. This is contradicted by other statements which claim that there are others that help and intercede for Muslims, like Muhammad even though he is dead.
If the dead like Muhammad can help and intercede this presupposes that the dead are still conscious and can hear invocations made to them. But other passages expressly deny that the dead can hear since a barrier called Barzakh separates them, and also states that the prophets have no knowledge of the people’s response to their message.
The Quran says that there is nothing comparable to Allah, which presupposes that there is no image which can be made of him. The Islamic narrations that say that Adam was created in Allah’s image and that the black stone is a symbol of Allah since it is his hand clearly contradict this belief since they prove that Allah can be depicted and does have (a) visible representation(s)."