Thank you, Robert. There's the problem, isn't it?
Some Christians refuse to see other Christians as Christians.
It doesn't matter that Mormons see themselves as Christian. Because you don't like their beliefs, they're not Christian. So simple.
So,
Is the Society of Friends ("Quakers") Christian? What about Mennonites? Episcopalians? Churches who preach Jesus is God, there is no Trinity?
Certain Christians believe only Christians go to Heaven, and then decide only Christians they agree with are Christian, so the group of people going to Heaven gets smaller and smaller, and the group of people going to Hell gets larger and larger.
And your god gets smaller as well.