Why do most philosophers insist that ethical principles should be universal? Can't I have my own private ethical code, my own set of principles, which I don't expect anyone else to follow, although I would not be against the fact that others follow it, that is, I'm not trying to be a free-rider or harm anyone. One of my principles might be: don't preach.

Let’s consider what it is for ethical principles to be universal. One way of understanding the claim that ethical principles are universal is to take it as the claim that the correct moral principles apply to all of us. Here’s one way to appreciate this claim. Suppose that a particular act, A, is morally obligatory for you (maybe it’s the act of not preaching to others about how they should behave). If that act is morally obligatory for you, but not morally obligatory for someone else, then there must be some relevant difference between the two of you that accounts for this difference in your obligations. There must be a reason why you have the obligation and they do not. Suppose the difference is some feature, D, which applies to you but not to them. We now have the principle: All those who have feature, D, are morally obligated to do A. Note the principle is universal. It applies to all of us, and says that all of us who have the same feature, D, that you do have the same obligation that you...