I can see it now.
Seriously though, Madnak is right about intelligence possibly having it's drawbacks in regards to reproduction. You can't just say "smarter people are better for the human race"
Also there are the problems with testing, etc.
And I'm curious why you said "Removal of the bottom 50% of each ethnic group" rather than just "Removal of bottom 50%." regardless of ethnicity. Is this to avoid accusations of race-based eugenics or is there some other idea?