We fear insanity.
Insanity makes people turn on themselves and others.
In insanity social rules are ignored. Like children, madmen just do not seem to understand the rules. Some psychologists argue that these childish behaviors, doing whatever they want when they want, worrying about food, etcetera, are repressed desires that we still possess as adults. After ingesting his potion, Dr. Jekyll separates into the two personalities of Jekyll and Hyde. Jekyll is honest, respectable, inherently good and Mr. Hyde is younger, deformed, and atrocious.