If the world became smart overnight

90% of it's population would realize how useless they are, and how, their not being there, would benefit the condition of the world, and kill themselves.

Then the remaining inhabitants would agree to breed once each life-time, every 40 years.

People buy what they like, and or what is useful to them.  Capitalism rewards those buisiness people who create products people like.  The profits they will make, their fame, and other things, will likely depend on this, as well as how well they run their business.  All transactions are voluntary. 

In theory, what the hell is wrong with that?

Capitalism rewards those who give the people what they want.