Paul Anthony Samuelson was an American economist influenced by John Maynard Keynes. Samuelson believed unregulated markets have drawbacks, he stated, "free markets do not stabilise themselves. Zero regulating is vastly suboptimal to rational regulating. Libertarianism is its own worst enemy!" Samuelson strongly criticised Milton Friedman and Friedrich Hayek arguing their opposition to state intervention "tells us something about them rather than something about Genghis Khan or Franklin Roosevelt. It is paranoid to warn against inevitable slippery slopes…once individual commercial freedoms are in any way infringed upon". Samuelson was likely the most influential economist of the later 20th Century.