What do you propose to do with paper? Mostly it just gets fed into a machine. Is it impossible to vote twice with paper? Is it impossible to throw away paper? Is it impossible to miscount paper?

Paper doesn't impart any security property by itself. Can paper be used in a secure system? Maybe. Can a machine be used in a secure system? Maybe. Is all paper secure? No. Is any machine secure? No. Same for blockchain, mobile, internet, satellite, and ouija boards.