What both of the previous posters seemed to have missed (or at least failed to write down) is this: If, as part of your religion, you truly believe that if you do not worship Zuul by saying the Lord's Limerick three times a day, that Zuul will punish you by having a giant Stay-Puft Marshmallow Man trample your fair city under his giant marshmallow feet, then wouldn't you try to have your all your friend worship Zuul too, so that their cities wouldn't be trampled in puffed sucrose and Titanium Dioxide?
In more obvious words, many people believe that for example, failing to introduce people to Jesus to save them from Hell is even worse than failing to throw a drowning man a rope.
So I can understand this type of behavior, it's perfectly logical, given the premise of a deeply held religious belief involving salvation of the believers and damnation of the non-believers. Well, for me, the premise doesn't hold water though, so...I guess it's Damnation for me then, at least according to some folks.)