The duty to stay could easily come to seem as pressing as the duty to enter. As long as we get out clean, the absence of debate doesn't matter much. Unlike Americans, the British, people as well as soldiers, are ready for action. Acquiescence in its possibly painful consequences is in the bones of a military nation. Up to a point, we probably don't mind about the absence of perfect clarity either.
Ministers dodge around that, and prevaricate when asked to be precise.
But people understand that war is messy and, within limits, are probably less fastidious than harrumphing editorialists who complain about mission creep. Thus far, they have been justified. Only a doctrinaire non-interventionist could complain about the rescue operation. History, in fact, supports something rather bigger. The place is, after all, our legacy.