Hmmm, well I think this would have worked just fine, mass murder and all. I think both the article writer, and some of the responders, seem to miss that comics have already involved a lot of teenage heroes and villains, including some who have been extremely murderous.
Given the number of Peter Parker's school chums/teachers who have become villains (at least temporarly) I could see a similar arrangement being done using the Batman rogues gallery in an alternative universe. I mean Catwoman isn't all that far away from Felicia Hardy (The Black Cat). The Joker isn't really all that far away from The Green Goblin who is ALSO a
mass murderer.
As far as giving it a whimsical spin, I don't think that's a big deal either. I look at characters like Deadpool, Ambush Bug, Slapstick, Squirrel Girl, and numerous others who manage to co-exist with and even cross over into more serious comics. It's really not that hard to have some really serious nastiness going on while also being somewhat lighthearted and casual about the whole idea. Indeed that's the kind of thing classics (or cult classics) are made of. I mean think of the whole Deadpool concept, especially when it first got going, complete with him breaking the fourth wall as a matter of routine. Ambush Bug is even worse and exists in the same world as The Joker, and Batman.