Joke's on you
WHAT IF................ the Legion of Super-Heroes took the Joker into the future? Could they cure his insanity?
The Martian Manhunter once momentarily cured Joker of insanity by filtering the impulses raging through his mind. Saturn Girl is at least capable of doing that. We know that in the 30th century, mental illness is almost unheard of. Star Boy's schizophrenia was easily controlled with medication.
Could they bring Joker to the future, learn his true identity?