I think perhaps the premise is misplaced. Christianity isn't finally about belief; it's about relationship. Heck, the Apostles were arguing belief and doctrine while Jesus was still amongst them -- who was most favored, who would sit at Jesus' right hand, etc. The corpus of Xy has never agreed with each other, except on one point: Jesus is Lord. How that plays out, is expressed, and is codified is another matter. Xy isn't supposed to be uniform -- only unified. It's supposed to be diverse, but not divided. I'm not aware of any major denomination that condemns all others. As Xtians, we're supposed to foster right relationship, not believe certain things about Jesus.