How do you recognise a false teacher or spiritual deviant who infiltrates the church?  Peter has already pointed to their heresies and lies (2 Peter 2:1), greedy exploitation of the vulnerable (2 Peter 2:3), filthy living and lawlessness (2 Peter 2:7), despising authority (2 Peter 2:10), arrogance and slander (2 Peter 2:10-11), blasphemy and ignorance (2 Peter 2:12).  They will not exhibit all of these characteristics, but all will show some.  

Now Peter uncovers their shamelessness. They just cannot stop sinning and even celebrate their sinful behaviour openly.  Even if they want to (and there is little evidence that they do), they are unable to stop polluting themselves and the churches they seek to influence.  Peter’s choice of words is dramatic: they stain what is pure and gouge what is smooth, revelling in sensual pleasures while sounding spiritual.  They always want what does not belong to them and captivate the minds and hearts of those who are easily led.   
 
Even in the context of the church fellowship, their appetite for self-satisfaction is unlimited, whether through drink and personal pleasures, or by luring the gullible into their web to satisfy their lust for power.  They use those who look up to them, rather than serving them.  Their expertise is in getting their own way at the expense of others; although any objective eye can see that their whiteness is so deeply stained that they have no right to participate in the fellowship meals, let alone lead them.  How different from the ministry of our Lord Jesus.  And how right He will be to bring harm to those who harm His Body (1 Corinthians 3:17).
 
Of course, apart from Jesus, there is no teacher or leader who can claim to be without sin.  So what is the difference between the false teacher and the leader who struggles with sin?  Firstly, their destiny is different: harm for the rebel and help for the weak.  Secondly, their attitude is different: the rebel is unashamed, while the weak sinner feels shame most deeply.  Thirdly, their lifestyle motivation is different: the self-righteous knows no repentance, while the penitent sinner longs for change and holiness (Luke 18:9-14).  So, if you are oppressed by 'spiritual people' who do not live by the truth, be comforted that God will deal with them.  If you are weak, be comforted that the Lord will restore the repentant.  But if you use God's people to indulge your own sinfulness, beware: do not wait any longer to repent before the Lord uses His hand!