Why do adults dress up as characters for Halloween?

Ann Althouse writes a post this morning in which she asks several very good questions. Here is one:

There must be some significance to the adult involvement in Halloween in present-day American culture? I don't think I've dressed up as a character for Halloween or any other occasion since I was a child, but I see my fellow adult Americans going in big for Halloween year after year. Why are we doing that?

Read more here.