When a person deeply intertwines themselves into their argumentation, you are given the choice to argue around them or at them, or you can just nod at them. It's very hard to attack someone's personal credibility without being "personally insulting", and that especially includes questioning whether true crime tv cuts it for discussion. How does one do that not insultingly?

That's why, whether the effect is desired, the final result is constraining. You cannot lower someone's credibility non-insultingly.