Sheb being a theocracy was naturally ruled by the priests, and priests are naturally bigoted in favor of their own narrow creed, and intolerant of differences of opinion on theological matters. It's really too bad that things are that way, but there you are: you have to take the world the way it is, not the way you would prefer it to be.
Chapter 4 (p. 56) - The Wizard of Zao (1978)