The truth is we all know when something is rotten. Some claim that changing situations make for changing morality—in different situations different acts are called for that might not be right in other situations. But there are three things by which we must judge an act: the situation, the act, and the intention.

The main argument relativists appeal to is that of tolerance. They claim that telling someone their morality is wrong is intolerant, and relativism tolerates all views. But this is misleading. First of all, evil should never be tolerated. Should we tolerate a rapist's view that women are objects of gratification to be abused? Second, it is self-defeating because relativists do not tolerate intolerance or absolutism. Third, relativism cannot explain why anyone should be tolerant in the first place. The very fact that we should tolerate people (even when we disagree) is based on the absolute moral rule that we should always treat people fairly—but that is absolutism again. In fact, without universal moral principles there can be no goodness.

The fact is that all people are born with a conscience, and we all instinctively know when we have been wronged or when we have wronged others. We act as though we expect others to recognize this as well. Even as children we knew the difference between “fair” and “unfair.” It takes bad philosophy to convince us that we are wrong and that moral relativism is true.

Of course, the psychiatric community doesn't really have a construct called "sanity" to begin with. There are mental illnesses which shade into adjustment difficulties which shade into appropriate adjustment; it's a continuum. Illnesses and disorders are far better defined than healthy psyches are, but the lines between them are artificial and arbitrary.

All we can do is our best: to understand ourselves and our inner lives and how those ingrained perceptions affect our interactions with the outside world. Refusing to accept that any such impact exists however is, in my opinion, opening the door to "insanity."