 What was the basic purpose of The Bell Curve?
The Bell Curve was not circulated in galleys before publication. Herrnstein and Murray didn't do this, so it wasn't until a full year or more after The Bell Curve was published that the leading experts on its subject had a chance to go through the underlying data with care. The Bell Curve refers in passing to some of these points, but on the whole it sets up a cartoon-left position as its (easy) target. Having conditioned its audience to view IQ as all-important, The Bell Curve then manipulates statistics in a way that makes IQ look bigger, and everything else smaller, in determining Americans' life-chances.
 to show that our government really can't help poor people become more successful
 to show that our government really can't help poor people become more successful  to get people to stop believing in IQ tests  to explain how to improve peoples' intelligence  to help people learn how to improve their social status