When communities face a great many social and economic obstacles to achieving their conception of the American Dream, there is a natural inertia or resistance when members of this social setting actually seek to improve their particular standing.  They are looked at with a dose of skepticism and misgiving combined with a certain level of envy and resentment.  Mrs. Johnson might be representative or symbolic of this.  Her visit and query into the Younger family's prospective move does not seem motivated by a genuine sense of wanting to see her neighbors succeed.  Her raising of the fear level by invoking fire bombings and racist attitudes of Clybourne Park are only done so as a manner to cause a level of discomfort in the Younger family's move.  It is evident that Mrs. Johnson is staying in the neighborhood.  Her visit symbolizes some attitudes that seek to "hold back" members of a community who seek to pursue independence from a particular social setting.  Mrs. Johnson represents the fears and doubts that plague the undertaking of such a change.  If you wanted to analyze it as a cliche, consider the following:  "There are a million reasons not to do something."  Mrs. Johnson represents that concept of the "millions of reasons" not to undertake risk in hopes of a better life.  It is interesting to note that Mama Younger showcases her sense of defiance and strength, something we have not seen before.  Perhaps, to show to Mrs. Johnson that she is committed to bringing respectability and opportunity to her family, Mama invokes the defiant and active side to fend off the aversions and doubt Mrs. Johnson casts.