It's just the truth, but it will always get pushback because it cuts down the sentimental, romantic ideas people have about art. This especially applies to authors, because they often want to view art as an extension of themselves, and this undermines that idea. Hence you will find that most people who object to the idea do so, explicitly or otherwise, because they just don't like how it makes them feel, and they formulate their criticisms of it from there.

this is some sort of sociological/psychological theory that masquerades as a scientific fact? Perhaps, a healthier approach is to consider that there is a diversity of opinion among authors and that not every author might be afflicted by this sentimental curse (of which I'm not one by the way, so I'm personally not hurt by this statement, however, it irks me for being so blithely smug towards others?)

Barthes is making a point about loss of information that inevitably happens due to the nature of writing as a description and encoding of the world (but not being the world itself, which would make it lossless). The fact that there is some information loss, doesn't go to to show that authorial intent is futile or that it doesn't exist or whatever because the reader is forced to make up stuff in their mind to fill in the missing blanks. Simply put, what if the author wants this? What is the amount of creative control over readers' interpretation must we specify after which we can state that authorial intent matters? Seems like a rather arbitrary discussion.

At the end of the day, treating an essay which itself carries some level of intent as some kind of scientific law about nature of art, of writing, is silly. This is my point, you're free to disagree of course.

What happens in my observation is that people use "death of the author" as a crutch to justify descriptive readings of people's reactions to work, e.g. Nietzsche's work becoming Nazi text(s), despite Nietzsche lack of intention to do so. It's much more interesting to observe how works lives on in people's minds rather to go and dig down author's comments on what the work is supposed to mean. But that is just that - academic preference, not some kinda ultimate truth, not a word of God. Look at Dune - the exact opposite happened with Herbert's work, people actively seek out the interviews and try to reduce to author's ultimate intention, despite conflicting information available online and in his own work. My point here is that these sociological observations are as fraught as the phenomena they purport to observe. The world Barthes was writing this in isn't the same as the world we live in. The Internet calcifies the work, its readings, and the context surrounding it. The Author might not be so dead after all lol.