Your criticism of Boushey boils down to dismissing as insignificant the distinction between relative and absolute advantage and a counterclaim that under capitalism whites and blacks and men and women all lose and ergo racism and sexism are in no ones interests, save maybe capitalists.
The LBO archive on the Boushey essay runs over similar ground and while I agree with you that racism and sexism are in not workers "interest" in some fuzzier meaning of that word, your doing little more that reasserting the primacy of class over race and gender. Which begs the question as to what racism and sexism represent and how best to combat them.
Dennis Breslin