Monotheism and Islam


Can all monotheists in the world (Muslims, Jews, Sikhs, Bahais etc.) be called Muslims?


No, not all monotheists are true Muslims, nor are all Muslims Muslim.
This is not a puzzle I assure you. To explain, we need to distinguish between the tag assigned to people saying "Muslim", and the content of the heart of a person which defines him as being a true Muslim or not.

A monotheist is simply someone who believes that God is One.
However, the majority of those who believe in the One God are also committing shirk:

The majority of those who believe in God do not do so without committing shirk.

Anyone who is committing shirk by definition is not a genuine Muslim. A genuine Muslim is someone who not only believes that God is One, but also submits to God alone in every sense of the word.
A person committing shirk is not submitting to God alone, but has other idols whom he allows to share some of God's exclusive rights.

We learn from 12:106 that the
"majority" of people in the world who believe in God are committing shirk, and thus they cannot be called genuine Muslims (submitters to God alone). The words in 12:106 apply to people of all religions, including Muslims.
Now let me show you another Quranic verse with some very significant words:

Abraham was neither a Jew, nor a Christian; but he was a 'hanifan' (monotheist) Muslim (Submitter) and was not one of the mushrikeen.

The question that must be raised here is:
If being a monotheist means that a person is also a Muslim, or that he is not committing shirk, then why did God add the words "Muslim. He was not one of the mushrikeen" after the word "montheist"?
Surely by saying "monotheist" this would have included being a Muslim who does not commit shirk? Or does it?
The answer is that being a monotheist is no guarantee that a person is a genuine Muslim, nor that a person is free of shirk.