What you say is true, because you can be a Christian and still sin. But I base this on my own faith. I do recognize that others' faith may differ from mine. I think they are wrong and they think I am wrong. True Christians have enough in common, or ought to, that they can still worship God together while disagreeing on things like how baptism ought to be done and whether the bread and cup symbolize Christ's sacrifice for us or actually become the body and blood of Christ.