That is a common argument... but just because a test is not "culture free" doesn't mean it's worthless. If we measure the IQ of the son of an immigrant Kalahari bushman and it's, say, 79, that is an important measure despite being "ethnocentric" (and quite frankly not everything that is specific to one culture is bad). It is still useful information when you want to know things like how well the boy will do in an American school system.
Does it mean he's stupid? Not at all... A skill set valued in the desert (let's say, fast reaction time and a concrete approach to problem solving) is simply undervalued in the school system here. Should we redefine the tests to suit his cultural background, where in all likelihood he will score higher, just to assuage whatever bad feelings we have? I think that would be pointless--whereas knowing that the child is NOT using those skills that we value in our society, those skills that tend to go along with good grades and a good job, is a useful thing indeed.
So yeah, if the ultimate goal of IQ tests is to put value judgments on people you're absolutely right. It is not fair to label the kid. But if the goal is to devise teaching interventions to help him succeed in our schools and in our culture it is kind of nice to be able to see where he is deviating from the norm.