How does Zinn argue that the Supreme Court cannot possibly act in a neutral fashion?

Zinn believes that they cannot be neutral for numerous reasons. One is that they are chosen by the president so they will usually be someone who fits the presidents political beliefs. Another is that their choice is ratified by the congress which can also dictate then who becomes the judge or not based on their political beliefs. Another way is that they are all extremely rich and successful lawyers and judges and that as solely members of the upper class they will naturally be biased towards it.