Metaethics for Atheists
Part of the reason for that misunderstanding may be because many atheists do in fact espouse the kind of relativist view that my critic finds objectionable. But the main problem is the over-simplification that is common in popular discussions and writings on this topic. Most people seem to think there are only two main positions one can take: absolutism/objectivism, which states that there are moral principles that are true for everyone at all times, and relativism/subjectivism, which roughly says that what's right for one person may not be right for another. What's worse, some atheists appear to associate the absolutist view with religion (in effect implying that if one adopts such a position, it is only because of one's religious beliefs), and as a result insist on relativism. And of course, the religious more often than not criticize atheism on the grounds that it is incompatible with objective values, and thus can only lead to relativism.
In addition to all this, the terminology involved isn't used in a consistent way even by philosophers. There are specific views which everyone basically agrees on the meaning of (e.g., non-cognitivism, emotivism, intuitionism), but some of the broader terms are definitely used in more than one way — and none more so than “subjectivism.” No wonder, then, that there is so much confusion.
