I've made this argument in the past, but this old campaign poster for William McKinley's 1900 re-election campaign makes the point better than anything I could say. What you see here -- "the American flag has not been planted in foreign soil to acquire more territory but for HUMANITY'S SAKE" -- would be perfectly recognizable as a neoconservative slogan. And yet, it comes from the period we now think of as involving precisely the effort to plant the American flag to acquire more territory, specifically colonies in Puerto Rico and the Philippines plus informal empire elsewhere.
And there's the rub; the much-vaunted "idealism" of the neocons is nothing new. And, indeed, I don't even think we should view it -- or the rhetoric of a William McKlinley -- as necessarily insincere. Rather, it's an example of the boundless human capacity for self-justification and self-deception. If you decide that military domination is the policy you want, you'll swiftly find a way to convince yourself that military domination is best for the world. Kipling called it the white man's burden, the French called it la mission civilitrice, and it's all equally meaningless however you want to phrase it.