A
quote from the
liberal theologian,
Martin Marty, stated during a
conference on the
role of
organized religion.
Unbelievers play a role similar to the multiple houses of the government - to provide checks and balances. Because a non-religious person isn't going to want to put up with a religion that is a burden.
When a religion attempts to remove unbelievers it is a sure sign of danger - a warning.