He learned Keynesian economics through a state sponsored school which supports government spending through inflation. That's why most economists think like him. It's highly likely he's brainwashed and he won't listen to you. I'd ask him how is it that America saw one of the greatest economic expansions under the gold standard without inflation. Might also point out that inflating the money supply is quite literally stealing and if your or I did it we go to jail. It's a moral issue, a system based on theft. However, deflation would make the current system blow up due to all of the debt, so that's part of the perspective he's coming from and I doubt he'll see out of that if he thinks Keynesians are the smart ones.