I follow Ebert on Twitter and while he has some good points usually (Damn, he's made a career of them) I think he's being a bit harsh. Is Kickass really as bad as A Clockwork Orange,Reservoir Dogs,Repo Man or a number of uber-violence flicks?
TBH, I think it's more the adult male view that little girls are made of sugar/spice. Dammit, Peter Jackson started off with Bad Taste & Brain Dead and NO-ONE can tell me they're not insanely bloodthirsty and violent. As well as being damn good fun.
What it satirises is the media, which he himself is a part of, that treats every violent action as "the downfall of society". Nip to some African countries and you'll experience that sort of horror on a daily level. Personally I'm glad that it offends some people, as it may get them to think long and hard about how sensitized we are to movie violence, but not to real-life wars.