How does Douglass use rhetorical questions to underline the contradiction of liberty as espoused in the Declaration of Independence and the legal practice of slavery?

In the following example, Douglass uses rhetorical questions to show that he, and others like him, have hope that America is in its infancy and in time will realize, as other, older countries have, that slavery is abhorant.

The eye of the reformer is met with angry flashes, portending disastrous times; but his heart may well beat lighter at the thought that America is young, and that she is still in the impressible stage of her existence. May he not hope that high lessons of wisdom, of justice and of truth, will yet give direction to her destiny? Were the nation older, the patriot’s heart might be sadder, and the reformer’s brow heavier. Its future might be shrouded in gloom, and the hope of its prophets go out in sorrow. There is consolation in the thought that America is young.