I have been a moral realist for as long as I can remember. I think the reason is roughly this: it seems to me that certain things, such as pain and suffering to take the clearest example, are bad. I don’t think I’m just making that up, and I don’t think that is just an arbitrary personal preference of mine. If I put my finger in a flame, I have a certain experience, and I can directly see something about it (about the experience) that is bad. Furthermore, if it is bad when I experience pain, it seems that it must also be bad when someone else experiences pain. Therefore, I should not inflict such pain on others, any more than they should inflict it on me. So there is at least one example of a rational moral principle.
Michael Huemer, Ethical Intuitionism, Basingstoke, Hampshire, 2005, p. 250