I don't understand the position of the MacBook. Back in the day "MacBook" was the entry level laptop for those who wanted a Mac. It was less expensive. As for the MacBook Air, I'm not really sure what will happen to it since "MacBook" is technically the lightest laptop. I would assume Apple to discontinue the MacBook Air in the near future.
This is the most probable course of action. The MacBook will replace the Air just as the retina MBP has (almost) replaced the MBP.
So why is the Macbook at the same price range as the MacBook Pro with a crappier performance? I find it kind of stupid.
Its not. The Macbook is the price range as the MBA. The rMBP is still more expensive. It might be stupid, but its just as stupid as having the MBP and the MBA.
Why would anyone sacrifice performance when you can get the Pro version at the same price?
Because some (actually, a lot of) people value portability over power. Educators, journalists, writers, scientists, consultants basically everyone that needs to move a lot with a laptop but does not work with processor-intensive applications. Hell, I would get one, but for my needs its really a bit too slow. Plus, I want to be able to play games on my work laptop