It goes something like this:

What the Joker was doing—what they were doing, together—was helping Alice understand himself better and accept himself more. It was important to him to do it, not just because he wanted to have that experience, but because he wanted to learn from it. Well, 'learn' might not be the best word. Try: he wanted to change in the ways that that experience made him change.

Apparently, his power was backing him on that.