As a newly converted Christian brought up in a non-religious household, I find this frankly confusing. Even with my limited Bible study, I know to love my neighbour, whatever their beliefs.
Rather than concentrating on the subtle differences in doctrine, why can't all the Christian sects acknowledge their great similarity - The belief in Jesus Christ and His salvation? Squabbling with each other seems to be such a waste of time.
Yes, there are people like the Jehovah's Witnesses and many fundamentalists who spread a false Gospel... But wouldn't it be easier to expose them if all true Christians - who value life whether it's American, Christian, Muslim, Iraqi or pagan - joined together to expose them? Frankly, American evangelists scare me.

There are proably plenty of reasons why various christians think that this is impossible - but they should remember that they all identify themselves the same way - as Christians.
Now maybe they should act like them.