In the course of his letter to Clay, Channing took a solid swipe at destinarian justifications:

"It is sometimes said, that nations are always swayed by laws, as unfailing as those which govern matter; that they have their destinies; that their character and position carry them forward irresistibly to their goal... that, by a like necessity, the Indians have melted before the white man, and the mixed, degraded race of Mexico must melt before the Anglo-Saxon. Away with this vile sophistry! There is no necessity for crime. There is no Fate to justify rapacious nations, any more than to justify gamblers and robbers, in plunder. We boast of the progress of society, and this progress consists in the substitutions of reason and moral principle for the sway of brute force. It is true, that the more civilized must always exert a great power over less civilized communities in their neighbourhood. But it may and should be a power to enlighten and improve.... We are destined (that is the word) to overspread North America; and, intoxicated with the idea, it matters little to us how we accomplish our fate. To spread, to supplant others, to cover a boundless space, this seems our ambition, no matter what influence we spread with us. Why cannot we rise to noble conceptions of our destiny?" (50-51)

Manifest Destiny: American Expansionism and the Empire of Right (1995)
Anders Stephanson