There are no moral absolutes, so you ought to stop judging the moral beliefs and behaviors of others!" A crucial flaw in one's views is when one makes a self-defeating (also called "self-refuting" or "self-referentially incoherent") statement.
What exactly is a self-defeating statement? It is a statement with three characteristics. (1) It establishes some requirement of acceptability for an assertion (or sentence, proposition, or theory). (2) It places itself in subjection to this requirement. (3) It fails to satisfy the requirement of acceptability that the assertion itself way, stipulates.
A statement is about a subject matter. The subject matter for "All dogs are mammals” is dogs. When a statement is included in its own subject matter and fails to satisfy its own standards of acceptability, it is self-defeating.
Some examples of self-defeating statements are these: "No sentence is longer than three words." "I cannot utter a word of English" (spoken in English). "I do not exist." "There is no truth." "There are no truths that cannot be verified by the five senses or by science.”
In identifying a self-defeating statement, we must exercise great care in making sure that the statement actually refers to itself, that it is a part of its own subject matter. For example, the claim that one cannot utter a word of English is not self-defeating if asserted in French. More importantly, the statement "There are no moral absolutes," though false, is not self-defeating. Why? The statement is a philosophical assertion about morality and not a claim of morality.
To be a claim of morality, an assertion must be a moral rule such as "Do not kill," "Abortion is wrong," or "One ought to be tolerant of others." "There are no moral absolutes" is not itself a moral rule. Like a statement made in English about all French statements (for example, "No French statement is longer than three words"), "There are no moral absolutes" is false. But since it is not included in its own subject matter, it does not refer to itself and therefore is not self-refuting.
Another important example is "There are no moral rules, so one ought to refrain from passing judgment on others." Is this self-defeating? It's hard to tell because the word ought is ambiguous and comes with different meanings: A rational ought occurs in "Given the evidence, one ought to conclude that the defendant is guilty." A rational ought places an intellectual duty on someone, and a violator is irrational, not immoral. An aesthetic ought occurs in "One ought to play this piece with great emotion." This places an aesthetic duty on someone, and a violator is guilty of failing to produce beauty. A moral ought occurs in "One ought to keep one's promises." This places a moral duty on someone, and a violator is immoral.
The ought in "There are no moral rules, so one ought to refrain from passing judgment on others" is either a rational or a moral ought. If the former, the assertion means "Given all the evidence, there just are no moral rules, so one has an intellectual duty to stop judging that others have violated absolute moral rules when there are none." Though false, this statement is not self-defeating because it is not itself an example of asserting a moral obligation. Rather, it asserts an intellectual duty, and a violator would be irrational, not immoral. But if the ought is a moral one, then the sentence is self-refuting: "There are no moral rules, so one has a moral duty to follow this moral rule-do not judge others."
Some statements, such as "2 + 2 = 7," could not possibly be true. Others, such as "There are no dogs," happen to be false but could have been true. Self-defeating statements do not just happen to be false; rather, they are necessarily false. For example, it is impossible for these statements to be true: "There are no truths" and "Only what is testable by science can be true." Among other things, this means that no amount of future research will show that a self-refuting statement was true after all. This is important, because a statement like "Only what is testable by science''can be true" is not itself testable by science, so a skeptic cannot say that, while there may be no current evidence for its truth, someday science will advance to the point of proving that it is true after all
Extracted from the Apologetics Study Bible.