I think what he means is...
Window cleaner is up the ladder washing the windows, ladder slips on an un-even surface. Window cleaner gets hurt and then claims off the customer saying "floor wasn't level" etc.
If this did happen they wouldn't have a ladder to stand on imo.
Oh, I understand perfectly well what the general idea of his argument is; it's just that the last sentence makes no sense to me. I agree with you; in my opinion it's the responsibility of the ladder user to make sure it's safe. If his judgment is incorrect and he falls, that's his own fault, after all, no-one made him use an insecure ladder.
