While I respect Elon for his accomplishments, as an AI enthusiast, I don't like his view on AI. My guess is that, he sees AI from physics and sci-fi point of view.
Max Tegmark, a famous physicist argues that AI is possible. http://www.huffingtonpost.com/max-tegmark/humanity-in-jeopar...
Just because something is possible in theory doesn't mean it is in practice.
Interestingly, many of the pessimistic views on AI come from non-computer scientists such as economists, physicists, and philosophers. I wonder whether they have ever actually read a textbook on AI or machine learning instead of just thinking at a high level. If they have, they should have appreciated how hard AI actually is.