It really isn't. Your goal should be to have no text, and never look away from your audience during a talk.
You can (and should) repeat key points, but every time you read, you lose your audience. And yes, you can have a little bit of text -- but since most people go too far in the other direction, it's best to aim to eliminate text entirely.
Slides should be simple graphical content to provide signposts and communicate things that otherwise cannot be expressed vocally.
I think you're overshooting in your advice in the service of preventing the bigger mistake of turning around and reading slide contents verbatim (on which I certain agree with you). That's fine, but for veteran presenters, I think your advice is wrong. First, you should have text because you lose your audience no matter what (sneezing, emails, bathroom, etc). You should let them recontextualize and that involves judicious use of text. Also, everyone asks for slide decks after talks and they should be useful in that case even without a recording. Lastly reading doesn't mean, "turn away from your audience and read", it is the same as repeating key points - this can be done for emphasis or pacing, as long as it's intentional. This is my opinion based on my experience, at least.
"Also, everyone asks for slide decks after talks and they should be useful in that case even without a recording"
I am happy to provide copies of my slides, but no, I am under no obligation to make them useful without me presenting them. They're my tools, not your reference.
IMO, this expectation has been driven by bad presenters leading people to believe they can get the same content without bothering to show up to the talk. Maybe that's true, but if it is, you should wonder why you're giving the talk at all.
If your slide contains a picture, whose details you're describing (say for instance a medical photo or city zoning plan or something), certainly you want your audience's visual attention on it as you're describing its pertinent specifics.
You can (and should) repeat key points, but every time you read, you lose your audience. And yes, you can have a little bit of text -- but since most people go too far in the other direction, it's best to aim to eliminate text entirely.
Slides should be simple graphical content to provide signposts and communicate things that otherwise cannot be expressed vocally.