I agree in many circumstances it's annoying and often they sound ignorant, but when they're telling you that you're going to hell, in many cases they genuinly believe what they're talking about and want to "save" you. At least from what my right wing Christian conservatives tell me...

Converting seems to be a problem when money is involved. For example Mormons require members of the church to send 1/10th (I think that's the fraction) of their income to the Mormon church. There is a perfect reason to have aggressive conversion stances...