Oh wait, he was one of the (ahem, so called) justices that ruled that corporations are people.
While this is accurate to say, it's like saying that he's one of the justices that is a human being. All justices, judges, and magistrates accept that corporations are legal persons. This is neither surprising, nor debatable, and is a fundamental part of Common Law tradition. Why are corporations people? Because otherwise, they couldn't own property, and could not be sued.
Let's have a hypothetical. Let's say that corporations are not people in our new world. Alice, Bob, and Charlie are working together in a Corporation, ACME. Now, ACME is not a person, so someone has to own all the assets that would otherwise belong communally to ACME, and the three decide that Alice should be the person of record for ownership of materials. Now, someone has to run the company and be on the line for any legal messes, and the three decide that Bob shall do the actual operations of the company, and direct Charlie in his work, while Alice just sits at home, and collects a paycheck just for not walking away with the money and property. Now, Bob tells Charlie to dump some toxic waste in Derick's yard. Derick is upset, and goes to sue ACME in court, however, since ACME is not a person, he cannot sue ACME. So, he has to sue the people responsible for the toxic waste dumping. Well, obviously, he'd like to go after Alice, with the deep pockets, but she had no hand in causing the harm. Bob would also be a nice choice, because as the director, he has a reasonable salary, and it was his policies that directed Charlie to dump the toxic waste. Except that Bob only ever told Charlie in verbal communication that was never recorded to dump the toxic waste in Derick's yard. Leaving the only person that Derick can sue as Charlie, who is really just a lowly employee with no salary, and no real power. Derick sues and throws Charlie into bankruptcy with the tort finding, while Alice continues to maintain all the company assets that have not been touched, and Bob continues to direct the company however he sees fit with no accountability for his actions.