Answer:
The notion here is discrimination based on the skin colour, specifically of black people in the US. This notion was previously expressed through slavery, and people think that it's ended, but this is not the case: black people are still opressed, socially and economically. This is unfair and cruel, therefore, it has to change. The long term result would be a full integration of black people into the society. The idea of racism and ethnic discrimination needs to change. In this speech, Kennedy is saying that in a country that calls itself free, even in the constitution, is not actually fully free. He makes remarks about how we can say to the world, "We are a free country!" ...Except for the Negroes. He also expressed how we can "Preach freedom around the world!" and then turn around and endorse acts of slavery and discrimination, without even acknowledging it, acting like doesn't exist. The idea of this discrimination needs to change in order to become a truly free country. Although we can as a country we can say we are free, egalitarian country, the citizens of such country may not express that.