Bitcoin is built on cryptography and economics, and Adi Shamir is an expert only in one of those fields. If he criticized the underlying cryptography of Bitcoin (which is not RSA by the way), that might have been a bit worrisome, but since he talks about economics, his prediction is as good as of any other random mathematician. All this negativity towards Bitcoin comes from people who don't realize the value of decentralized digital money, and sadly it makes them think that Bitcoin is a bubble.