Slaves+Rights?

Arguments/reasons for extending rights to slaves:

"After 1840, abolitionists denounced slavery as not only a social evil but a moral wrong." ( http://en.wikipedia.org/wiki/Origins_of_the_American_Civil_War, 09/21/2011)

" In a sense we've come to our nation's capital to cash a check. When the architects of our republic wrote the magnificent words of the Constitution and the [|Declaration of Independence], they were signing a promissory note to which every American was to fall heir. This note was a promise that all men, yes, black men as well as white men, would be guaranteed the "unalienable Rights" of "Life, Liberty and the pursuit of Happiness." (King, M.L., http://www.americanrhetoric.com/speeches/mlkihaveadream.htm, 09/21/2011)