What is wrong with discrimination?

Usually, we think that a discrimination is morally wrong if it is based upon prejudices or biases, the incorrect judgements of lesser moral worth of some persons. But that thought has two problems. First, a liberal society can not always recognize a discrimination based on prejudices as a morally wrong discrimination. And second, the discrimination based on biases hides the fact that some discriminations are not based on biases. So, to avoid both problems, we should define the morally wrong discrimination by their effects (effects on the equality of opportunity) on the victims rather than by the reasons (biases or prejudices) of the discriminators.