Why is it relevanant if he wanted to extend or not? And what does it matter if you are a believer in these things or not. The point is, he was sold something and paid full price for it, yet did not get the complete package.
Would you be happy with purchasing a house, only to find the plumbing is only done to one of your two bathrooms?
What you need to understand is that if Sauron does not believe in it then it is wrong. Period.