In A Raisin in the Sun Mama refers to Booker T. Washington and also George Murchison as, "fools" because they both only care about the inside of the box, they don't care about what's outside. Like when George says "You read books—to learn facts—to get grades—to pass the course—to get a degree. That's all—it has nothing to do with thoughts." on page 97. They don't see the importance of going to school, of getting an education. They just look at the general point of view, not the detailed point of view. Both of them were trying to help the Blacks, but failed miserably, trying to change the way life was.
Mama knows that Blacks are of "lower class" compared to the Whites, however she calls them fools, due to the fact that she knows this knowledge. So she calls them fools even though she knows why they are trying.