One would hesitate, for the most obvious of reasons, to dispute astrophysics with a Nobel Prize-winning astrophysicist, but the case is quite otherwise with a Nobel prize-winning economist. This at the very least suggests a difference in the intellectual difficulty, rigor, or foundation of the two sciences. Common sense will not get you very far with black holes or antimatter, but in economics common sense is a necessary if not a sufficient quality in him who would think about it.
There is one group that is not protected from hate-speech: the rich. Of the rich it is permissible, and in some circles de rigueur, to speak disparagingly or hatefully. This, I imagine, is because it is widely supposed that if you hate the rich you must love the poor, and love of the poor, at least in theory, is the highest virtue. Unfortunately hatred is a much stronger political emotion, and vastly more effective in practice, than love was, is or ever will be.
That the rich are not protected from hate-speech proves that the one thing that speech codes are not designed to reduce or prohibit is hatred: for it is a distinctly moot point whether race hatred, or hatred of the rich, has been responsible for the more mass murders in the past century or so. The crimes of egalitarianism have been enormous; and so denigration of the rich is as disreputable, permissible or impermissible, as the denigration of many other groups I could name.
But who are the rich, apart from those shallow and grasping people with more money than I?