Instability invites the nastiest folks to take charge. When a governing structure lacks legitimacy, it has to use disproportionate violence to stave off anyone else who wants to take charge.

This isn't a moral defence of Hamas' attrocities. Saying asbestos cause cancer is not defending the morality of cancer; it is saying that if you want to avoid cancer you should avoid asbestos. Until the Palestinians have a stable government it should be expected that the most radical segments of the population will inflict violence. The median Palestinian is innocent, unless you think it was their fault for being born in the wrong place.