Blind or obsessive love may make a person unable to criticize or accurately observe their object, and we do see that in fandom. But what I see in you and many other emotionally mature fans is more akin to devotion - in much the sense of Middle Ages religious scholars who criticized the Church because they loved it, or patriots speak up about problems in government because they love and are devoted to their country.

How much of that "no cosplay" aspect is about wanting professionals to appear professional, do you think? Or about wanting creator A to not appear to be critical of creator B (or supportive of creator B) by wearing their costume? And yet I've seen creators wearing T-shirts and the like supporting others' works. (And a fine thing it is when a T-shirt is professional but dressing like Ianto isn't. Tsk.)