I'm fine with Nolan's Joker not having much back story. It adds to the whole enigma of the joker IMO. The guy is just crazy. Insane. Just does **** for the lulz.
I prefer it when Jokers backstory is blur & unknown. Pretty much the reasons you said. The guy is a friggin nut job
Yea I think certain characters like the Joker benefits much more from having an unknown past...to me it's more terrifying to think someone is simply born bat **** crazy than had some event turn them that way. Why...well I guess given the perfect storm of circumstances we all have it in us to loose our minds, but to think someone never had their sanity to begin with is an entirely different ball game.