[mrb]

Cash works, so hardware wallets will work.

See, people are used to, and are already pretty good at securing valuables such as cash (in a safe, at home, or on themselves). A paper backup presents to additional complexity to store securely. And Bitcoin offers extra advantages: losing your paper backup does not affect you ability to use the wallet, and you can have multiple backups, etc. So a hardware wallet is at least better than or equal to cash in terms of security.