The problem with Mermaid is not that she gave her voice to someone who shouldn’t. Not that I thought a couple of beautiful legs was all it took to get a beautiful prince. Not even that she is an ordinary romantic fool who thoughtlessly sacrificed her life, duty and family for the hope of love of someone she hadn’t even known. Everything is more prosaic.
Her problem is that she was also illiterate to everything else. Know how to write Rusalock at least in printed letters, even with mistakes - the fairy tale would have been completely different.