Kyle came off as impossibly naive and goofy in Hitman, but does okay for himself in JLA/Hitman. Granted, everyone in the latter book is kind of a dick except Kyle and Superman.
Ennis admitted in an editorial for Bleeding Cool a couple of weeks ago that one of the reasons he doesn't take American superheroes terribly seriously is that he grew up reading Judge Dredd. Superheroes agonize about maybe killing one guy; Dredd vaporizes five hundred million and gives no fuck.