The logical fallacy in sentence 5 is an ad hominem attack.
Explanation:
[1] Pediatricians who have children of their own take better care of their patients. [2] Being a parent or guardian is a powerful and profound experience. [3] It changes doctors and gives them greater insight. [4] Doctor Stevenson disagrees with my argument. [5] However, his judgment is untrustworthy, since he is not a parent.
An ad hominem attack is when you personally attack a person rather than the argument itself.
