What is the central idea of this excerpt from "The Destiny of Colored Americans" by Frederick Douglass?

The white man’s happiness cannot be purchased by the black man’s misery. Virtue cannot prevail among the white people, by its destruction among the black people, who form a part of the whole community. It is evident that the white and black "must fall or flourish together." In the light of this great truth, laws ought to be enacted, and institutions established--all distinctions, founded on complexion, ought to be repealed, repudiated, and for ever abolished--and every right, privilege, and immunity, now enjoyed by the white man, ought to be as freely granted to the man of color.

Where "knowledge is power," that nation is the most powerful which has the largest population of intelligent men; for a nation to cramp, and circumscribe the mental faculties of a class of its inhabitants, is as unwise as it is cruel, since it, in the same proportion, sacrifices its power and happiness. The American people, in the light of this reasoning, are at this moment, in obedience to their pride and folly (we say nothing of the wickedness of the act), wasting one-sixth part of the energies of the entire nation by transforming three millions of its men into beasts of burden. What a loss to industry, skill, invention (to say nothing of its foul and corrupting influence) is Slavery! How it ties the hand, cramps the mind, darkens the understanding, and paralyses the whole man! Nothing is more evident to a man who reasons at all, than that America is acting an irrational part in continuing the slave system at the South, and in oppressing its free colored citizens at the North. Regarding the nation as an individual, the act of enslaving and oppressing thus, is as wild and senseless as it would be for Nicholas to order the amputation of the right arm of every Russian soldier before engaging in war with France.