I am sorry, it is not a question of being stupid.

The issue is that a regular user doesn't have any clue about cryptography, public/private keys etc. However each of them would understand to cancel transaction which didn't originate from them, providing they'd have the chance.

It's about making adoption of Bitcoin easy for everybody.
If the adoption will require too much of knowledge especially about security, as it does now, then the wide spread adoption won't happen.