JackSantino, Ph.D. is an academic folklorist... (wikipedia)
People might want to shy away from being the ax murderer. Gore is still seen as unacceptable. Adults are hoping to break the rules and do a little wish fulfillment.
That 'I cannot tell a lie' has almost become a proverb. It's something that turns the patriarch of our country into a mythical figure.
In some parts of Europe, they'd look for bears.
Generally speaking, the whole point of adult masquerades is that you get to do something that you don't normally do.