The case McDonald v. City of Chicago presents to the Supreme Court the issue of whether the Second Amendment right to bear arms is applicable to state and local governments, or instead is only a right that Americans have against the actions of the federal government. Specifically, the question is whether the right to bear arms applies (or is "incorporated") to the states through either the Privileges or Immunities Clause or the Due Process Clause of the Fourteenth Amendment.
On November 23, the ACRU, joined by three other organizations, argued that the Second Amendment should be incorporated to the states through the Privileges or Immunities Clause, and that this should be done without overruling the Slaughter-House Cases. The Privileges or Immunities Clause could be used as a source for judicial activism unlike anything America has ever seen. The best safeguard against that possibility is the Slaughter-House Cases, which severely restricts the scope of that clause to only incorporate rights that are inherent in federal citizenship and that are grounded in the text of the Constitution. Since it is possible to incorporate the right to bear arms through Privileges or Immunities without overruling Slaughter-House, that becomes the safest way to extend this right against the states, while not opening the door to unintended consequences.