I would question that they are Christians if they deny that the Bible is the Word of God. Nominal, liberal, pseudo-Christians should not be confused with the real thing. Evangelicals have a high view of Scripture. If it is not the Word of God, we have no basis for Christianity. Do these so-called christians also deny the Deity and resurrection of Christ? If so, they are definitely not Christians.
Many atheists and agnostics have also made the same observation. There have been many debates on this forum about this matter.
What confuses many who examine Christianity is the way some Christians believe the bible to be the foundation of Christianity and others don’t. It makes more sense to me to see the bible as a collection of ideas written by man. Christianity based solely on faith in an invisible Jesus is much harder to pull apart.
Until there is agreement on this matter, the Christian message will be lost on most people.