What message does The Help send, in terms of injustice and the nature of humans in terms of injustice?

The message that The Help sends in terms of the nature of humans who face injustice is that people will fight against injustice any way they can. The characters in the book who are African-American domestics in Jackson, Mississippi, in 1962 are in a position of very little power in the white society, but they often find ways to fight injustice. They aren't allowed to speak back to their employers, but they find other ways to express themselves. For example, Minny, an African-American maid, gives Miss Hilly, a white woman who uses gossip as a weapon against the maids, a cake laced with feces. More importantly, the maids work with Skeeter, a sympathetic white woman, to construct a narrative of what their lives are like, providing insight into the lives of African-American domestics to an audience outside the south. 

Skeeter and the other women also work against injustice against women. Though Skeeter is pressured to get married, she decides instead to work as a writer and refuses to get married just because it's conventional. There are many layers of injustice in the society portrayed in the book that involve race, gender, and their intersection, and though the characters are affected by these societal power dynamics, they also find ways to work together against them.