Re: 18% of this world's population is Muslims
I'm not going to argue about the figures, they're about correct.
However your assertion that Islam has been rejected by those who are not muslims is misleading.
If what you say were true then everyone in the world has been invited to the fold of Islam and then made a decision to refuse - this is patently not the case.
Besides, even if the majority HAD rejected Islam there is nothing in Islam that says the validity of Islam is to be judged in proportion to the numbers of its adherents.
So yes only one fifth of the world are muslims but I am not going to lose any sleep over this fact! :)