The Bible makes it perfectly clear that anyone who behaves this way will destroy themselves. They'll either be taken from this world suddenly, without a chance to repent, or they'll end their lives in misery. As Christians, we must pray fervently for their salvation, because these people are very much in need of our help. Psychologists call this aberrant behavior malignant narcissism. But God's term of "fool" is much more accurate.
Fools have reached the age of reason, so they know right from wrong. They are not crazy, nor are they out of touch with reality. They have full use of their faculties, and they are choosing to do evil rather than good.
The Book of Proverbs is especially rich in messages to ponder about the folly of taking a wicked path. There's no doubt it leads to destruction. In the first chapter, there's a clear message that fools "set a trap for their own lives." In Chapter 12, we are told the "schemer" is condemned by God, also that "the wicked are overwhelmed with misfortune."
Knowing this makes it much easier to forgive someone who has harmed us at church. That's because these individuals need to seek God's forgiveness. With any hope, our fervent prayers will give them the grace to do that.
It's tempting to want to settle the score ourselves. But let God handle it. Fools eventually convict themselves in the eyes of the world. This happens because people who suffer from malignant narcissism don't know when to stop, as they are not operating under the influence of the Holy Spirit. So they push things so far that their former allies begin to turn on them.
For additional reading on malignant narcissism, and how people with this disorder do not know when to call it quits, please visit my Female Bullies blog.