He defines his identity ("I am a retributivist") according to philosophical stance rather than to simply describe his beliefs ("I ascribe to retributivism").
> "To be clear, I oppose family punishment. Why? Because I am a retributivist."
That's not an explanation. The answer "I am a retributivist" does not answer "why?". The natural next question is "What led you to retributivism?"
Once your political or philosophical stance becomes your identity ("I am a conservative." "I am a progressive.") it becomes extremely difficult to accept alternative information or perspectives that might change your mind. It becomes extremely difficult to even bother justifying your stance. "I vote straight line Democrat because I am a Democrat" "I vote straight line Republican because I am a Republican"