You're right that some moral philosophers have tried to find irrefutable principles as a foundation for ethics. Maybe they have been naive or dogmatic in their assertions. But you may be dismissing the search for principles to quickly. How do we know that your view - that there are no principles and no foundations - isn't just another dogma? A postmodern dogma?

It seems to me that the search for principles is a necessary part of moral philosophy. Look, if we make any ethical judgments at all, someone can ask why we make that judgment in one case but not in another case. That forces us to be more general and add qualifications. In other words, it forces us to move toward a statement of principles. The only way to avoid that is to push the question off the table. But if we have a commitment to rational discourse, we can't do that.