Perhaps. I propose a larger sample size. FOR SCIENCE!
V for Vendetta: social commentary $132 million worldwide.
Watchmen: social commentary $184 million worldwide.
I would say that both of them are arguably better overall movies than TDK as well. I think so, at least. TDK isn't an especially challenging movie when it comes to commentary. Like I said, I'm not even sure what side the movie takes. You could argue that the way it handles the social commentary is to provide an in-road for either side. "It's wrong to do this" "but it's necessary to do this". That's both sides of the issue right there. And the movie does both of those things.
As for the idea of society breaking down, at the end the movie says "the people have show you that they're not gonna stoop to that level!" The audience says "you're god damn right! We're awesome like that!", but earlier in the movie they had people shooting at and attempting to murder an unarmed man through a bomb threat. People are totally willing to stoop to that level that day. I think that movie sends mixed signals. It's far too busy being an engaging story about a crazy guy trying to make everyone else crazy along with him, and all the commentary stuff is just tacked on. You can basically ignore it and have the exact same movie at the end.
Spiderman 3: no social commentary $890 million worldwide.
Ironman 2: no social commentary $623 million worldwide.
Of course watchmen was also rated R and had a giant blue glowing penis in many parts of it, so the comparison of box office isn't necessarily fair.