It sounds as if Buterin has admitted that smart contracts are not very smart, or very useful in the real world. The existence of Plasma indicates that Poon and Buterin believe that a lot of work needs to be done before Smart Contracts are ready for mass use.
The hope behind Plasma is to increase the scalability and speed of Ethereum smart contracts. Like Bitcoin, Ethereum has a serious scalability problem, currently a block of Ethereum can only execute around 20 transactions a second; or 1,200 transactions a minute. That makes it impractical for large-scale commercial applications.Read more