Because it is not the business of the law to make people feel good especially not at the expense of others when that expense encroaches on the Bill of Rights. To make people feel good by force of law is to chase an impossible goal, the subjective feelings of those to whom the framers of the law pander. Once the subjective feelings of any group are exalted into the force of law we have abandoned law for the rule of the mob. Every time you sacrifice the right of free speech to spare the perceived feelings of some minority or other, you will never cease sacrificing my rights because that majority will never cease contriving ways to have hurt feelings.
Nearly as bad, to do so would be to institutionalize hypocrisy on a national basis. When you can show me white people (or black people, in reverse) who do not daily practice discrimination, I will assume they have passed on to a better place. When we choose a neighborhood to buy a house, or to rent an apartment, we consider school system, whether it is white enough. When we go for a walk we avoid black areas because they are more dangerous. When we go shopping, we pick whiter areas in which to shop for the same reason. Every day in a million ways we make conscious and unconscious decisions based on discrimination. It is beyond the capacity of law to control the way think. It can try, it can resort to unbelievable totalitarian brutality in the effort, it can construct and even use ovens, it can construct and consign millions to gulags, it can expropriate media and bombard the people with propaganda but at the end of the day the wall always falls. Even if it were a worthy goal, the cost in human suffering, as history has proved, is exorbitant and not worth the illusory goal.
Every day, I discriminate on the basis of race and so do you. I discriminate on the basis of a lot of things which may or may not be irrational but that decision remains within my own personal sovereignty and not to be disturbed by law. Just because the law has taken other rights to discriminate away from me, for example the right to rent an apartment only to people of a chosen color, does not mean the law should or can compel me to vote for or against a candidate because of his color. There are limits to the desirability as well is the power of government to control the way people think. There is a vast difference between depriving me of my right as a landlord to discriminate on the basis of color and taking away one of my bill of rights to indulge in "hate" (an ultimately undefinable concept) speech. If we can do that, can you compel me to worship a black Jesus, can you compel me to worship in a black church? Why not? Think of the greater good!
The ultimate purpose of laws of censorship are to control the way people think, the ostensible justification is always some alleged public good.
