"It is an absurd notion that there are two manners of discussing how the pie should be divided up"

There is absolutely a difference between normative and positive statements about the world. Arguing whether raising taxes will lower middle class wages is a different question from whether one should raise taxes.One is a question of facts and the other is a questions of values. This distinction holds no matter what field you are discussing; it's just the field of economics where people seem to insist on blurring the two.