Pappy’s snarling, slur-spewing villainy verges on caricature, but “Mudbound” does not pretend that his is the only, or even the most insidious, face of white supremacy. Nor does the film locate the poison of racism principally in the attitudes and feelings of the dominant race. What Hap and Florence are up against as they try to provide for their children and hold onto their dignity is a system of organized expropriation — a heritage of plunder (to borrow a term from the writer Ta-Nehisi Coates) designed to keep them poor, precarious and dependent. Their labor provides an insurance policy for Henry’s bad luck and incompetence. Their successes will be punished so his failures can be mitigated and his entitlement upheld. What’s theirs is his.