It's a contentious cult... they might as well be Wiccans, because rebellion against God equates to the sin of witchcraft. And they lie against God's words, telling sinners that they cannot be saved - and they also do behavior which is contrary to what the spirit of Jesus would do. If they tell people that they are beyond God's ability to save because they are sinners, then they are deluded into thinking of themselves as being righteous without God. We are all sinners, and the role of Christians is to point people to Jesus, so He can make us faithful to Him, discern righteousness, and be children of the truth.
For rebellion is as the sin of witchcraft, and stubbornness is as iniquity and idolatry. Because thou hast rejected the word of the LORD, he hath also rejected thee from being king. - 1 Samuel 15:23, KJV
Paul spoke of such people:
“The one preach Christ of contention, not sincerely, supposing to add affliction to my bonds:” - Philippians 1:6, KJV
Paul had the right spirit about it, he was humbled calling himself the chief of sinners, realizing that it was only by God's grace that he was accepted by Him. Paul understood grace and mercy very well, and this is why he elaborated so well on it in the book of Galatians, Romans...etc...