Nudity and The Law

Nudity in art is commonplace both in historical and contemporary art. So the curator must understand what is and is not law abiding so informed choices can be made. Indecent Exposure is illegal however, as a retired police officer with over 30 years experience noted, " Unfortunately I don't know what indecency means - and neither does the Law - so a decision as to what is indecent is usually left to a Magistrate or Jury."
Is this why hysteria sometimes follows nudity, because no one really knows where the law stands or is it something else?