Have you seen the size of these classrooms? It's not uncommon for lecture halls to seat 200+ students. You're thinking that each student is going to present? Are they all going to create a presentation for each piece of info they learn? 200 presentations a day every day? Or are they each going to present one thing? What does a student do during the other 199 presentations? When does the teacher (the expert in the subject) provide any value in this learning experience?
There's too much to learn to have people only learning by presenting.
"Let them cheat"
I mean, yeah, that's one way to go. You could say "the students who cheat are only cheating themselves" as well. And you'd be half right about that.
I see most often that there are two reasons that we see articles from professors who are waving the warning flags. First is that these students aren't just cheating themselves. There are only so many spots available for post-grad work or jobs that require a degree. Folks who are actually putting the time into learning the material are being drowned in a sea of folks who have gotten just as far without doing so.
And the second reason I think is more important. Many of these professors have dedicated their lives to teaching their subject to the next generation. They want to help others learn. That is being compromised by a massively disruptive technology. the article linked here provides evidence of that, and therefore deserves more than just a casual "teach better! the tech isn't going away"