It is a trite yet urgently true observation that if America is to remain a first-class nation, it cannot have second-class citizens.
Martin Luther King, Jr. (1929-1968) American clergyman, civil rights leader, social activist, preacher
“The Negro and the American Dream,” speech, North Carolina NAACP, Charlotte (1960-09-25)
(Source)
King used this line in several of his speeches at the time.