With HTML, I can do everything as a <div> and the eyeball reader doesn't know/care. Where it matters is that I'm stripping semantic meaning, which hurts computers and possible accessibility devices.

Most of my life, the same has been true about dashes. I use - for every one of the kinds you provided because - lives on my keyboard.

Is there real value in caring? Does it have the same semantic—stripping effect for computers/accessibility devices? The part of me wondering if I really should care is trying to suss out if this is a real problem or just an argument for semantics pedantics.

I can't think of any case where a human gets confused by some text because a hyphen character was used instead of an em-dash, and maybe that's what you mean by real value.

But I see you using an em-dash to hyphenate "semantic-stripping" as a joke, which is funny. Is that real value? Is conveying to others that you're educated real value?

Only when responding to rants, i.e. pedantry for fun. Live a little!