Lane has various problems with the character who calls herself Hit Girl. He thinks her swearing is a cheap trick to generate buzz. He thinks her presence turns the movie into "cartoon violence" and makes the movie appeal to children. He thinks that viewing it will make children mistake savagery for slapstick and so "coarsen and inflame" them. Underlying all his other criticism, he thinks she's pornographic. While not being able to provide any evidence, Lane is preoccupied with her sexuality; he even says that she is "the dream of every pedophile."
To be clear: the little girl in question doesn't dress provocatively. She doesn't act provocatively. There's nothing sexual about her. If the actress had been 12 or 13 she might have had budding sexuality, but Hit Girl is thoroughly a child.
Lane tries to argue the pornography angle by saying that that the difference between a sexualized child and a violenc-ized child is a "false dichotomy" and a "cowardly distinction". I think he's engaged in some fuzzy thinking there. There is most definitely a difference between a child who is sexualized and one who is violent: there is no child-violence-voyeur equivalent of a pedophile.
There is one major similarity between children who are sexualized and who are violenc-ized: both situations give the child a sense of empowerment but are ultimately damaging to them. But for a pulp fiction movie, the movie is very sensitive to the child's problems. The movie makes it clear that this is one very damaged little girl. She was raised by an insane revenge-obsessed father who made killing a game. When we first see father and daughter, they are standing in a culvert and he is repeatedly shooting her in the chest with a large hand gun (we then learn he's teaching her to get used to her new bullet-proof vest). At the end, she is placed in a safer environment.
The difference between a movie about a sexualized little girl (and there have been many, from Lolita to Pretty Baby to Taxi Driver and on and on) and a movie about a violenc-ized little girl, is that millions of little girls are sexualized but few in the Western world are turned into Ninja fighters. There isn't a social issue here.
There is shock/novelty value. There may have been an 11 year old pig-tailed assassin in fiction before, but I can't recall when. And Lane is right that the Hit Girl character might appeal to kids - but this is an R-rated movie. As long as a movie is rated appropriately, I don't see how you can criticize its effect on kids.
I can't believe that Lane would have had such strong objections to violenc-izing a little boy. His review, at heart, is just old-fashioned disapproval of girls being action heroes. And he's really, really bothered about it - to the point that he expresses disgust with people who disagree with him - and to the point that he misses the good stuff in the movie.
The actress who plays Hit Girl, Chloe Moretz, has an impressive resume even though she was 11 at time of filming, and she did a brilliant acting job. When she says "Oh daddy, I'm just fuckin with ya", it's a show-stopper. She doesn't swear much in the movie, but when she does it's the best swearing I ever heard. She is convincing in a role that most actors would make laughable.
On top of all this, Lane and many of the other reviewers I read just don't get the movie. It's about the yearning and futility of wanting to be more than you can be. The character who calls himself Kick-Ass wears a baggy mail-order Hallowe'en costume and makes zero progress in becoming a superhero. He has a wealthy classmate who is able to buy a more convincing costume but does no better at the superheroing. Hit Girl is the closest we get to a human superhero, but she's ultimately just a little kid who's over-eager to please her dad. Even at the closest they get, when Kick-Ass dons a jet pack and flies himself and Hit Girl across the city, they have still failed to cross the line between being a superhero and just pretending.
In the short form of the review that appears in later New Yorkers, Lane writes that Kick-Ass "has the makings of a pointed - and much needed - poke at comic book afflatus, but the satire backs away all too quickly." Again, he misses the point. Superhero movies tend to play with the edges of the genre, exploring it and examining its internal flaws, but you shouldn't expect them to satirize and criticize the genre. The superhero genre simply isn't serious enough for satire to have any relevance.
Except for her age, Hit Girl is has a lot of similarities to Uma Thurman's character in Kill Bill, and Kick-Ass owes a lot to Kill Bill. If I hadn't liked Kick-Ass I might have thought it was too derivative. But I wouldn't have blamed it on the kid.