Mind-control. That’s Mad Hatter’s game. And while The Joker played a mind-control game of his own with Batman in The Dark Knight, the Mad Hatter (a.k.a. Jervis Tetch) would have other plans of controlling every mind in Gotham City if he were in a movie, possibly with another airborne chemical or hallucinogenic like the one Scarecrow used in Batman Begins.
We can’t see Nolan relying on a character using hats to control people. That’s just a little silly and too outlandish for Nolan’s world. But who knows? Maybe Nolan would even make the whole Alice in Wonderland complex that Tetch has work. He made Scarecrow work after all, and that was no small feat.