The vast majority of the poor are part of the basic proletariat (yes even if we are on welfare). We wait tables, clean houses, cook the dinner you at a few nights ago, harvest the crops and live in those run down shacks and trailers on the outskirts of town.
Like any other class, we can be reactionary or not. We can also be revolutionary and none of this comes spontaneously. If we are racist jerks, we learned it somewhere and if we are Communist, we learned that somewhere, too. It comes through our social experience.
BTW, there are many poor southern whites, especially youth (yes-in those run down trailer parks and other places) that are actually anti-racist.