The problem, Caww, is that again and again, the area of contention concerns justice - what did the child suffer for?
http://www.apologeticspress.com/articles/3400
The argument isn't whether a giver of life taking back what it gave, is unfair. Rather, the argument is about the child that was agonised until death for absolutely no fault of its own. Is mere death the same as suffering + death? No.
Even Jesus' death wouldn't have been the same without the suffering element. What did the child suffer for? Was that justice? No.
The apologist misses this completely, and provides support to the argument that it take superstition for reasonable people to justify evil. If killing children in the name of preventing them from committing sin later on is a justification, it is of the vilest of all possible human acts one can indulge in.
Ok then...are you certain the child suffered?
Only someone who thinks it's "just" to kill one's own children so they don't commit sin, or for someone who kills his own daughter for having shamed the family (mercy killing) can a sadistic killing of David's innocent son be justice.