The rhetorical question "Are the great principles of political freedom and of natural justice, embodied in that Declaration of Independence, extended to us?" primarily contributes to the passage's central idea in the following way:
B. It reinforces the idea that the rights given to others are not extended to Black people.
This question highlights the exclusion of Black individuals from the principles of freedom and justice that are celebrated in the Declaration of Independence, emphasizing the ongoing injustice and hypocrisy of the nation's ideals in relation to the lived experiences of enslaved and free Black people.