If you are insisting that one can only be brilliant if he or she agrees with you, that’s obviously a silly argument. Heck, Karl Marx was brilliant; Proudhon was brilliant; Comte was brilliant. Heck, Bill Clinton was probably one of the naturally smartest guys to hold the presidency. That doesn’t mean they were right.
Obama is an exceptional writer, a gifted speaker, and displays an unusual amount of self-knowledge. Call it brilliant or not, but crying affirmative action is ridiculous. Obama should be opposed not because every black liberal is somehow by definition an AA baby, but because his liberal policies will lead to increased dependence on government, a perpetuation of the abortion holocaust, and a weak foreign policy.
But in practice there is still the fundamental distinction between having one's thinking properly oriented towards the good vs. mere cleverness. Obama strikes me as very intelligent and well intentioned but ultimately merely clever, not brilliant.
Think of it this way: how much more remarkable would Obama be if he truly understood economics and the Constitution instead of mouthing leftist platitudes.