Yes, 4 gives the atheist the benefit of the doubt that they are not a sociopath as stated in 5.
Paragraph 5 merely reveals that "moral subjectivist" is a contradiction in terms and violates the law of non-contradiction. Morality presupposes an objective standard. Subjectivist excludes such a standard. Both by definition. One cannot be both at the same time. A cannot equal not-A.