What makes you think there can only be one? I thought there was one santa claus, for years, until I found out that it was made up. Why can't there be many Gods, you have no proof to suggest there is only one, apart from some scriptures and a strong feeling that makes you feel good.

I am not saying you are wrong, I am just struggling to come to grip with the fact that one can only believe in one God, if millions of people believe different things, one can only assume that somebody get's it wrong. Are you not better off believing everything what is out there, until proven wrong? Why discredit all those other religions....
The fact is, humans have shown to be able to belief in anything whether it is bogus or truth.
Only facts can prove a belief system wrong.
And unfortunately facts quite often turn out to be estimations of the truth.