Exactly. For security reasons, you have no other option, even if it's rude.
But the opposite should also be true. Don't scream 'disloyalty' when a employee wants to leave on a short notice.
And FWIW, I tend to agree with your comment regarding loyalty -- that ship sailed long ago, 1980s, possibly 1970s.
In many places (in the world) you are expected to for months after you are laid off. In many european contries, layoffs must be announced a long time before they happen (a maximum number but not specific jobs).
In any event, you are expected to be loyal to the employer.