First of all, I compared Pain & Gain favorably to Kick-Ass 2. In Pain & Gain we get a bunch of douchebags who just don't know what to do and eventually kill someone. They must face the consequences though and beside some questionable aesthetic decisions by Bay, for his (or anybody's) standards he's not glorifying these murderers.
Secondly, the Lindsay Lohan remark is meant to be a little joke, I have much more faith in the mental constitution of Moretz, although some of the stuff the filmmaker is putting her through is arguably nothing I consider suitable for a 15-year old.
The attempted rape scene is one of the most disgusting and upsetting I've seen in a while. Cinema hit its low point here. Rape is nothing I'd make fun of, yet Kick-Ass 2 plays it for laughs (which is an inexcusable thing, I don't want to know how a real rape victim would feel watching this sequence as the real horror is totally downplayed in favor of a teenager who can't get his dick up).
I agree with you, that they started strong. The "superheroes" who are doing community service, regular guys wearing masks and capes and getting the shit beaten out of them if they're not careful - that's a moral lesson. Continuing with your vigilant crimefighting after swearing to your father you'll stop (who died because of your actions in the first place) - not so much. There's no character arc, at the end of the day neither Dave nor Mindy seemed to have learned anything. Mindy just runs away - which means she broke her pledge to Marcus that she'll stop crimefighting and her pledge to her dead father that she'll protect the city. Dave on the other hand continues even though his father died due to his actions and his arch-enemy did too.
The death of Chris D'Amico was another scene that really upset me. He doesn't wanna get saved by Dave so he decides to practically commit suicide by punching the one hand that holds him atop of the roof. He then falls and in the seconds of his fall redeems himself and survives by landing inside a fishtank, only to be eaten alive by a shark. That's disgusting and mean-spirited.
I understand that this should be ironic and that it's intentionally over-the-top, but it just misfires. That happens, Kick-Ass 2 just goes to far in killing innocent random people for the amusement of one rich kid. To most deaths there's not even a suspense arc, they just happen, thus the filmmakers don't value human life. Right, this happens in every other film nowadays, but the Kick-Ass 2 just does it the wrong way. In an almost pretentious way it presents itself as something artsy, stylized and more sophisticated than your average blockbuster. It tells us so often that it's NOT one of these brainless superhero movies that it's just so more severe that it actually turns out to be exactly one of them.
I missed character arcs and appreciation for human life. The message of the film is questionable - it intends to be a statement against senseless violence and modern desensitization but turns into an abomination that supports the exact values it originally stood against.