By making light of sinful behavior telling others that it's not possible to lose salvation even if they turned away from the Lord to live in sin - they are advocating that living in sin does not cause one to be separated from the Lord (spiritual death)
This is a trick of the devil that causes others to stumble teaching them believe they are still saved even if they continue or go back to living in sinful behavior. It's false doctrine that beings death (separation from the Lord)
It's the same thing the devil did with Adam and Eve in that he told them they could disobey the Lord and not die
The new testament warns about this:
Romans 8:13
For if ye live after the flesh, ye shall die: but if ye through the Spirit do mortify the deeds of the body, ye shall live.
And then they bark about claiming this is works salvation as they miss the part that says "through the Spirit" as they don't know how to submit themselves to the Lord allowing the Holy Spirit to work thru them
If they did they would stop their sinful behavior and would stop teaching heresy