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.
There's the keyword.
And that day is not today.
Paper is fine. Let's use paper.
These voting machines that can be tracelessly hacked with a pen drive are terrifying, and no, there isn't enough awareness of that fact among people.