I find the David and Bathsheba account difficult. However the existence of the human race was at stake and Christ needed to come in a certain manner. God isn't answerable to us. What man hasn't commited adultery in his heart.
"And certainly, having a child die is punishment of its own kind"
I think most parents would gladly trade places with their children if they were to die.
I think that Uzzah was unclean and God is Holy.