Ripping Hollywood for on-screen child mistreatment is a pet project of mine, so it was with some consternation that I found myself getting a kick out of "Kick-Ass."

Its breakout character is an 11-year-old superheroine named Hit Girl (Chloe Moretz), a vigilante with a purple bob and a plaid skirt who goes after mobsters with knives, guns and kung fu.

It's all good fun until somebody gets hurt, and in "Kick-Ass," everybody gets hurt. Including Hit Girl. There is a creepy and probably unforgivable scene at the end of "Kick-Ass" when a bad guy, a grown man, gets the drop on her, and belts her repeatedly in the mouth (this R-rated movie is NOT for younger teens, though it's pitched to them).

You could argue that the rest of "Kick-Ass" is an elaborate excuse to turn a little girl into a punching bag, a lowering of an already inexcusably low bar.

Or you could argue that director Matthew Vaughn simply loses his footing at the end, and that for most of "Kick-Ass" his high-wire act does an impressively good job of balancing good fun and bad taste.

Since this newspaper just snagged a Pulitzer and we're all drunk on champagne, we'll go with the latter.

And give Vaughn his due - bubble-gum black comedy (from a Mark Millar comic) is a tough tone to manage, and he mostly hits the mark in "Kick-Ass."

The title character is a nerdy teen named Dave (Aaron Johnson), a comic-book freak and virgin (is that redundant?) who impulsively decides to sew his own costume and take to the streets.

He calls himself Kick-Ass, but gets his ass kicked. These days, of course, pathetic failure is no obstacle to fame, and when a cellphone video of his one-sided street fight goes viral, he becomes a celebrity - fluency in New Media dynamics is one way the movie shows its smarts.

"Kick-Ass" also understands comic-book physics - for every superhero, there is an equal and opposite villain, and Kick-Ass' fame inspires the son (Chris Mintz-Plasse) of a mob goon (Mark Strong) to create a corresponding adversary.

The movie's real wild card, though, is Hit Girl, a qualified ass-kicker who feels sorry for the inept Kick-Ass, and intervenes on his behalf - she bails him out at a drug dealer's lair in an explosion of cartoon violence (and music choices) that marks the movie's high point.

Once Hit Girl appears, the movie is hers, and we eagerly follow her own peculiar story, which has to do with her apprenticeship under a trainer-enabler-psycho father (Nic Cage).

The movie's variable attitudes toward Kick-Ass and Hit Girl seem opposed. Does "Kick-Ass" satirize superhero wannabe-ism? Does it pander to it?

Maybe both. It plays out like a gender-bent, punk version of "The Man Who Shot Liberty Valance," horsing around with notions of myth, reality, bravado, reputation and authenticity.

There are times when Vaughn doesn't seem to understand the mixture himself. What he does understand, though, is casting.

"Kick-Ass" dies without the right Hit Girl, and strikes gold in the beguiling Moretz, who jumped out at audiences in a small part in "Diary of a Wimpy Kid." Here, she's properly in the spotlight, and shows off her grown-up presence - she understands the outrageousness of the movie's tween commando premise, and has the comic chops to find the right, facetious note during the intimate father-daughter chats about assault weapons.

She has nice chemistry with Cage, who has recently rediscovered the loopy screen presence his fans knew and loved. Judd Apatow vet Mintz-Plasse is just right as Red Mist, nerd villain counterpoint to nerd hero, and Clark Duke is on comfortable terrain as Kick-Ass' wiseacre friend.

Word to the wise, though: This is not for all tastes.