Why do religious people always think they are utterly right?

Today I had to call at a house as part of my work as a building surveyor. The householder was polite and affable, but when I left he insisted on handing me a religious tract, and got quite peeved when I refused it. This has happened a few times before, at Christian and Muslim households, and it seems to be the case with many such religious people that even if you say you are an atheist, then that is merely a signal for them to redouble their efforts to convert you to their view. It's almost as if by replying that I don't believe in God, or Jesus, or Mohammed, or Allah, or whichever mythical deity/prophet they follow, that I'm somehow criticizing them. Or do organized religions not allow contrary opinions to their own doctrines?