Why do societies so often see their own culture as the only correct one?

religion is subconscious. people may believe religion is a way to "spread the word of god" bla bla bla....but in reality its not. whether people know theyre doing it or not, religion is a way to make everyone be the same. people instinctively feel threatened by something different since they cannot understand it. by spreading THEIR religion, you are convincing other cultures to be like your culture and erase the unknown. considering christianity is popular with missionary work, its a way to spread western ideology. make some other culture like us, with our thinking, our way of government, etc etc. its a good way to spread power.