>there is not agreement on what Christian belief _is_
this isn't true at all. It's quite simply an Abrahamic religion based around following the teachings of Jesus Christ. There are plenty of different doctrines and interpretations but you can tell what is and isn't a Christian church.
Same thing with Daoism. Daoism is both a religion and a philosophy with very specific teachings and traditions. You can argue about how to interpret it, but that's not what pop philosophy books like The Tao of Pooh are doing.