Dr. King notes that one of the great obstacles to integration is the apathy or complacency of white "moderates" who supposedly like the idea of civil rights in theory but oppose it by inaction.

Translation: they talk the talk but don't walk the walk (which was a dangerous walk, to be sure).

Take a look at this quote:

I have almost reached the regrettable conclusion that the Negro's great stumbling block in his stride toward freedom is not the White Citizen's Counciler or the Ku Klux Klanner, but the white moderate, who is more devoted to "order" than to justice; who prefers a negative peace which is the absence of tension to a positive peace which is the presence of justice; who constantly says: "I agree with you in the goal you seek, but I cannot agree with your methods of direct action"; who paternalistically believes he can set the timetable for another man's freedom; who lives by a mythical concept of time and who constantly advises the Negro to wait for a "more convenient season." (19)

This seemingly well-intentioned talk from white moderates could have an nasty effect by sapping political will for radical change, encouraging Blacks to keep their heads down, and placing faith in the idea of the inevitability of justice. This kind of so-called moderation was, in effect, the segregationists' best tool.

Then there's the concept of extremism. Because Dr. King and his supporters were constantly smeared and accused of being extremists, he decided to embrace this term and turn it around on his critics by saying, "I gradually gained a measure of satisfaction from the label. Was not Jesus an extremist for love[?]" (24).

This simple turn reveals the weirdness of the idea that whatever is called "moderate" is inherently more reasonable than whatever is called "extremist." This is one of Dr. King's important ideas: that justice requires people fighting for what's right, no matter what labels are thrown at them.