What's the greatest sacrifice anyone could make? Their life? Nah, they've got something much more important. Their soul.
Now if you do something evil, tainting your soul, or even irrevocably damning you to Hell for eternity, but the reason and result was for good, then it's possible that you just made the greatest sacrifice in the name of good that anyone ever could. You gave your soul so that others may be saved.
To illustrate my point, here's an example:
Say that I had a child, and somehow I found out that my child is THE Anti-Christ. True blue, take over the world and make everyone suffer Anti-Christ. I decide to murder my child so that he will never rise to be the Anti-Christ. If this actually ended the threat of the Anti-Christ (and didn't just postpone it until he was born as another child), then I've literally just saved EVERYONE from the worst fate possible, and by committing an utterly evil and reprehensible act, murdering my own child. It doesn't matter that he's going to be the Anti-Christ, he's still just a child, with no understanding of good or evil or any of that stuff. I murdered an innocent child, my own to boot. I am surely damned to Hell, where the soul of my child and I get to spend eternity together, only I'm being tortured the entire time.
But in sacrificing my soul, I have saved the entire world from the Apocalypse and the resulting suffering and destruction that comes from it. Good wins by default, and there is no need for the great battle between good and evil, meaning no war, less useless suffering.
So really, by committing these evil acts (and I don't know the specifics for any except the Shackled City one), could it be possible that their personal self sacrifice might just be the "goodest" thing they could do?
If the "Late, Great Planet Earth" described Anti-Christ properly, its first "miracle" is surviving what should be a fatal wound to the head. If were to attempt to murder the child and failed, you would not be postponing or cancelling the Tribulation and Last Judgment, you would hasten it.
At any rate, you'd probably remove whatever marked the kid as Anti-Christ out of sheer pity -- the kids at school would be teasing him mercilessly about that strange birthmark. End of Anti-Christ, no deaths.