The joker isn't the disease in Gotham, he's the symptom. In a world where the effort of an individual results in proportional gains, where people have a home, family, and attachments to their community, there is no joker. The populace is innoculated against his desire to tear it all down, because they have a stake in "it all". The few that are vulnerable to his views, are getting the support and care they need from trained staff, and the people around them are keeping the joker away. Batman isn't in Gotham because of the Joker; the Joker can exist in Gotham because of Batman, a billionaire who spent his efforts and resource on violence, instead of outreach.

Plus, giving OSHA some teeth, and forcing corporations to compensate fairly for workplace accidents, and regulations requiring the inspection and certification of toxic chemical plants would have stopped the joker, and countless other tragedies, at a fraction of the cost.