And the need to use special libraries to handle objects that have been strings since the dawn of Unix is precisely the kind of mess the poster is talking about. Yes, yes, everyone agrees that these problems "can" be solved in Python. The question treated is whether or not Python (and modern utf8-centric string libraries) solves them WELL.
Similarly once you’re talking about output other than passing it through unmodified to a format which can handle that, you are by definition converting it and need to handle what can go wrong. It’s easy to handle this in several ways, either by reporting an error or using some sort of escaped representation with an indication that this doesn’t match the document encoding, but you no long have the luxury of pretending that treating string as a synonym for bytes was ever safe.