Let me thrown in something further.
From what I understand, it is stated in the Quran that to believe in the Christian God (the Trinity) is an unforgiveable sin.
Furthermore, say that Islam is the right religion, wouldnt it be upsetting to God that one is worshipping the Triune God everyday? Hypothetically, is it possible that if there is another god instead of our God, that he could be getting more and more angry at our “pagan” practices and beliefs. Therefore it is possible that it would be better if one was “neutral” (a non-believer).
To add to this, some Christians claim that if they don’t accept Jesus as their personal Lord and Saviour they won’t be saved. Now, what if the gods of other religions held this view? What would lie in store for those worshiping a false god to the true god?
Finally, if one would worship a false god (without knowing it, of course), how is it technically any different to worshiping money, power, idols etc? I mean they would all be false gods.