Real Mermaids Don't Wear Bras

I'm struggling with a concept here -- maybe my aversion to political correctness. I can't put a finger on it. The comment "Real Mermaids Don't Wear Bras" is a statement on a bigger issue. If you put a bra on a mermaid, for instance, you change the mermaid into something she's not. You don't have a mermaid any more. What am I trying to say here? Someone read my mind.