I guess you are talking to me? If so, you read into what I wrote what I have never written. I have never suggested that you embrace the OP, or become friends with them. I see no reason to trust an ex-spouse or their A partners with your personal life or your love life. I certainly wouldn't.
My point was merely that the OPs are no worse than the ex-spouses. They are equally to blame. They are equally redeemable. They are equally forgivable. Demonizing the OP is generally largely about putting one's anger someone. It is better placed on the ex-spouse as the true betrayer of the M in that it was your ex-spouse who had an additional specific duty to protect YOUR M.
If one's children are safe around the ex-spouse, they are probably safe around the OP. You may not like it. But, unless there is a chance of real emotional or physical harm from OP, it is far beyond your control. Continuing to have a problem with it only harms all involved, including you, and most of all, your children. You put your children in between the parents in a harmful way for the sake of an R that no longer exists.
D is hard enough on children without figuring out how to love the other parent and their partners without you feeling betrayed. Don't make your children's Rs with the other parent and their partner about you. Those current Rs have nothing to do with an M that no longer exists. Treating them as if they do makes it impossible for a child to be happy with all the important adults in their personal lives without feeling like they are betraying you. In this way, you continue to make your children pay for your ex-spouses A. Not fair.
And, really not justified. The A partners aren't evil demons anymore than the ex-spouses are.