If it's not returning to old ground, arc, I think your rationale is as hollow as the "world's policeman"—if it's not that very argument in new guise—because that unconditional surrender was to the United Nations task force, not to the US.
The USA could hardly claim to be acting to maintain the UN's surrender terms in defiance of explicit UN resolutions denying the use of force and continuing the inspections. Thus the 'necessity' of trumping up the WMDs—"Look out, he's gotta gun, he's gonna shoot"—to justify shooting first, when the real policeman's saying, "Stay cool, we'll handle this and no one will get hurt."
lang, who raised the "world policeman" argument has apparently retired, but I'll ask this hypothetical question anyway. Hitler: By 1939 known badguy, bully and thug, well-known to have killed many of his own people, including Jews, and having intentions for more of the same. The League of Nations impotent. Suppose Joe Stalin had obtained the agreement of one of Germany's neighbours to stage from there—Poland would be as handy as Saudi Arabia was to Iraq—and invaded "because [Hitler had] killed (and was in process of, no two decade delays here) thousands of his own people"? Suppose the Soviets had pledged to stay until the German people had rebuilt and a true People's Democracy was secured?
Sounds to me awfully like the argument put forth at the top of this thread. Doesn't one self-appointed WP beget another? Care to comment? Or do we leave that for …?
In case you care, I find the scenario as objectionable as what did occur (sameresult, but after many more millions died). But I'm intrigued by those who would defend what I see as a very similarly objectionable action, just "because it's us". But then I shouldn't put words in other people's mouths. Maybe they'll say, "Get'im Joe!"