Based on the behavior displayed by some in the church, you'd be justified in concluding that they hold many folks in contempt, even others who claim to be fellow Christians but don't believe and practice the same things. When you think you are in the business of identifying and pointing out the faults in others, such negativism is inevitable.
If concurrently these same religious folks feel obligated to convert others to their religious thinking, it presents a real problem. How in the world can you effectively work to convert the very same ones you find so contemptible? If you don't want to associate with certain types because to do so might cause my own state of religious superiority to be jeopardized, then your conversion efforts are limited. You would likely want to handle the converting process at arms length by indirect means, like TV, radio, and books. Actually meeting the potential converts face to face would be too uncomfortable and even dangerous.
Christians hear both the call to evangelize and the need to keep themselves unspotted from the world, all from the same pulpit. Many choose to go with the latter. That sounds a lot better. Avoid sin by shunning the sinner. Makes perfect sense. More sense than Jesus!?