It is an absurd notion that there are two manners of discussing how the pie should be divided up - one objective, scientific, fair-minded etc., and one "political". Obviously it is all political.
As it was originally called - political economy. The term economics was promoted by Alfred Marshall, one of the most political of those focused on the economy.
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.
economics isn't a deductive science. i prefer Keynes' irreducable uncertainty as a principle of policy. we can't predict the future, we don't how policy is going to act out. the future won't look like the past. the chicago school's knightian uncertainty is the supply side of the same coin
there are flaws in the logical positive approach, see pragmatists like john dewey, hilary putnam, or richard rorty: https://www.youtube.com/watch?v=oLJfEVu3kbY