If one can acknowledge how all the denominations of Christianity manufacture their own interpretations of scripture to define their own understandings and how all of these interpretations are manufactured by men, they are all fallible to begin with. Even the Nicene Creed which was developed by man 300 years after Jesus died, has been changed and adapted by man.
Bottom line, if a person believe in Jesus as God and they are seeking outside acceptance of them being a true Christian, there will always be certain groups, telling them they are not, because they don't follow the same exact creeds as they do.
Beliefs are personal phenomenon and those who seek approval of theirs from others, likely are insecure in their beliefs. The same would also apply to those groups telling those who disagree, they don't belong.
Dear man, I am very happy to see you posting here and sharing your opinions with us.
However, I kind of wonder how you, an atheist, could understand how precious the basic tenets of our faith are to those of us who are Christians.
It is true, we have endless debates over such things as whether or not to play an instrument in the worship service, how wet one must get before he/she is baptized and whether it is important that he be dipped backwards into the water or may he go face first, what day is the Sabbath and what day we ought to worship, how often we should take the Lord's Supper...oh, a myriad of such minor details that people tend to get emotional over.
However, there are a few basic things that every Christian holds dear...one of these is that God is unique. There is only ONE God. There can be no other beside Him.
Another is the Godhead, or what is commonly referred to as the "Trinity". As it teaches in the Gospel of John, Jesus was with God from the beginning, and Jesus is God. Nothing was created without Jesus, and through Him was everything created. He is the Word, or Logos...in a sense, He is the power of God. Jesus is Divine. The Godhead also includes the Holy Spirit...that part of the Godhead that literally comes to dwell within every Christian. It is the Holy Spirit that writes God's law within us, as was promised long ago by the prophet Jeremiah. That prophecy was fulfilled on the Day of Pentecost.
Now, I understand that, as an atheist, you do not believe/have no belief/do not hold a belief in any gods, and I am not trying to convert you here. I kind of like you, actually, and it does make me a bit sad that you have decided as you have, but I have too much respect for you for that.
I'm just trying to point out to you why it is that traditional Christians do not accept Mormons, with their notion that God was once a man who was born on another world and who was elevated to his godhood by the god of that world, who obtained his godhood in the same way from yet anther god, who...ad infinitum.
And why traditional Christians also do not accept JWs who believe that Jesus is "a god"...totally separate from God the Father, Jesus is a sort of "lesser god".
Hopefully, knowing this will help you to understand us a little better....