It's not a matter of my opinion ... but, rather, the position settled upon here (USA) long ago by 'the powers that be.'
Our electrical codes apply only to the permanent wiring. Extension cords are not part of this, so the relevance of the NEC is quite limited.
In short, we expect the user to have a certain amount of sense ... rather than try to 'nanny state' everything into being completely idiot proof. It's a rather basic part of American culture.
