Passage Summary: Even though a doctor's diet book helped people lose weight, the author shouldn't have published it because the advice was unhealthy, and as a doctor, they should have known better.

Conclusion: MacArthur should not have published the diet book.

Reasoning: The book's dietary recommendations were harmful to health, and as a physician, MacArthur should have been aware of these negative health effects.

Analysis: This 'Principle Justify' question requires a rule that bridges the gap between the doctor's knowledge of harm and the moral judgment that the book shouldn't have been published. The argument establishes that the advice was bad and the author was an expert who should have known it was bad. We need a principle stating that if an expert knows (or should know) their advice is harmful, they are obligated not to share it. The most effective principle will link the status of being a physician and the potential for harm directly to the conclusion of 'should not have published.'