When the opponents of Jesus turn up accusing him of being in league with Satan (Mark 3:22) he doesn't so much as deny it as play with it. It is not the ones we humans expel as evil/immoral/ etc who are in league with Satan, but the accusers (who believe themselves to be righteously casting out Satan) who are in league with Satan, the great accuser: Satan casting out Satan. (3:23)
This dynamic of expulsion is played out among us and through human history. It seems good and right, even necessary to expel. And its effects of a temporary peace (by expelling the supposed source of conflict/sin) reinforce and support the sense of virtue retained/regained. But this peace is temporary, for a house divided is inherently unstable. (3:24-26)
And Jesus will ransack the strong man's house by first disarming him, like a thief. (Mark 3:27; compare Matt 24:43, 1Thess 5:2, 2Pet 3:10, Rev 16:15) The strong man is Satan, and he will do this on the cross. Satan will cast out Satan, and Jesus, in the disguise of a criminal and immoral person rightly crucified, the lie of accusation will be unmasked and God's vindication of Jesus in the resurrection will give us eyes to see.
This is scapegoating, Satan casting out Satan. When we participate in scapegoating we are in league with the diabolical. Of course, we all think we would never do such a thing. No one ever does think that, we always think we are innocently and righteously identifying the problem (someone else). All kinds of self-righteousness accrue. Social causes are vulnerable to being pulled into the diabolical. (Its why someone always ends up against the wall when the revolution comes.) Whatever you think of the righteousness of a pet cause (to say this should immediately give pause), the conditions for just such scapegoating are visible around us.
The lie that allows humans to be content in self-righteousness is best maintained if the scapegoat is guilty of something. That way the fiction of their (whoever they are) guilt can have at least an air of credibility. Scapegoating pops up as sides and causes are taken, and as victims (of evil) and perpetrators (of evil) are discovered and denounced. Satan casting out Satan. As mentioned, it is best if there is some element of guilt present and some element of ostensible (self-)righteousness. But the guilt need not be related directly to the 'crime', only tangentially. But when the invective rises and continues to rise, when we are all forced to take a side, or when to not take a side is to be accused of being on the wrong side of history (siding with evil), Satan is casting out Satan.
Following Jesus asks us to be sensitive to the victims of the diabolical who are innocent of the crimes heaped on them (not necessarily innocent). To be a follower of Jesus is to renounce the false peace and feelings of righteousness that flow from Satan casting out Satan. At a minimum, to be Christian and part of a Christian community is to find our communion in love and forgiveness, not in expulsion.
