Why is there so much deception involved with religion?

Virtually everything a Christian, a Jew or a Muslim says about their religion contains a certain level of deliberate dishonesty, right? They withhold some vital piece of information, they mislead, they misrepresent, they exploit, they corrupt or they just blatantly lie! And yet these people, these "religious people," have the gall to act like self appointed moral guardians, protecting society from immorality. I think it's their own willful deceptiveness that contributes the most to immorality in society. What do you think?