From a Canadian news site...
No. An obsession with professional sports, celebrities, and reality television arguably makes us dumber--both collectively and individually.
Ebooks do not make us dumber. An ebook is only a format for conveying the printed word. No more, and no less.
That's a bit like asking, "Do paperback books (vs. hardcovers) make us dumber?"
(Paperback books, by the way, were greeted with similar fears and skepticism when they appeared in the early 20th century.)
And for goodness sake: Almost no one is suggesting that this needs to be an either-or proposition.
I love my Kindle, but I still prefer hardcover or paperback when I'm reading a large nonfiction book that includes lots of maps, diagrams, and pictures. (As a rule of thumb: If I'm going to use a book as a reference tool, I prefer to own a physical copy.)
But for novels and shorter works of nonfiction, it is nice to be able to carry around so many volumes on my Kindle.