The segregated South was a culture of total racial oppression. So yes every aspect of the culture reflected and reinforced racial oppression, all backed by the threat (or reality) of violence. This doesn't cast doubt on the value of politeness, any more than it casts doubt on the value of signs, schools, water fountains, restaurants, or laws.
It shouldn't cast doubt on the value of politeness, but it does cast doubt on its application and where and why it is appropriate. Are you saying that this legacy has not cast any shadows on modern culture?
