And that is why we should kill all the jews. Utilitarianism is simply stupid as a moral theory. It ends in murder. Always. It cannot accomodate diversity of thought or personage.
please explain why maximizing the world's happiness is a bad thing.
Utilitarianism is a collectivist ideology where "the greater good" is used to justify violence against individuals. It is inherently evil.
Individuals naturally try to maximize their happiness, but once this becomes mobs of people trying to maximize happiness for everyone else, it simply ends in disaster.
Just look at how Mao or Stalin "maximized" happiness for the Chinese and Russians - hundreds of millions of people were murdered in the name of creating a "better" or "happier" society. When forced on people, Utopia invariably becomes Dystopia.