How can anyone claim to be a Christian while denying the divinity of Jesus?

Some religious denominations say they are Christian yet believe Jesus was only a man (even if a perfect man) when on earth. Some say he was Michael the Archangel before he came to earth in human form. Some say he was resurrected as a spirit creature. I can't find any basis for this in my Bible. Can you be a Christian if you don't believe in the divinity of Jesus when he came to earth?