This is the second time the Garveys' barn has burned down (accidentally). The first time was in season four's "The High Cost of Being Right".
Jeff Corey stars as the judge hearing Jud Larrabee's trial. He would return in season seven's "Blind Justice", this time as the accused, on trial for swindling the townsfolk of Walnut Grove in a fake land deal.
The Constitutional ruling to which the judge refers is likely the Civil Rights Act of 1875, which was specifically designed to protect ALL CITIZENS in their civil and legal rights including prohibiting exclusion from jury service.