From my understanding the POTS "sidetone" was a hack around handsets/headsets that too effectively blocked other sounds. What people really want are "transparent" headsets that don't block too many other sounds in the space the person occupies, or block only the "wrong" sounds.
I've watched enough musicians do sound checks to know that monitors are often more for hearing other parts of the band for coordination. Common requests are to lower the volume on their own instruments or eliminate their own instruments/voice from the mix in their monitor and stronger highlight their rhythm section or harmonies. But of course it varies heavily from artist to artist (which is why soundchecks exist and can take a lot of time, no single solution for everyone).
While television studios have had all sorts of reference monitors, no one ever called film and movie studios "unprofessional" and they still call their playback/reference monitors "dailies" for a lot of good reasons, even now that they aren't shooting on actual film anymore and they don't need to wait for film prints at the end of the shooting day anymore.
It's not unprofessional to want to avoid immediate, rough feedback and prefer an executive summary at the end of the day, even if the technology exists to do things immediately.
> The good news for you is the ability to turn that feature off! So what's the complaint?
Good news, there's an entire linked article here that includes many of the complaints. Partial, poor tl;dr: there is a rising mental health battle happening because of such "default features" of constant self-camera monitoring. The article here includes several strong reasons it should make more sense to default these features to off and let people opt-in to them rather than opt-out. General mental health and wellbeing is a good enough reason to change defaults. Also, in the comment you replied to with sarcasm, I added the complaints that even if these default on features weren't deleterious to mental health, they are distractions that often impact people's focus and attention spans in meetings. I also think that's a strong reason to default these features off, though it is still a lesser reason than the mental health issues.