> striking down Washington D.C.'s handgun ban by a 5-4 vote, the Supreme Court's decision in D.C. v. Heller held for the first time that the Second Amendment protects an individual's right to keep and bear arms, whether or not associated with a state militia.
This ruling is the crux of the matter. And ACLU's interpretation (against it) seems very logical. Sadly there's no putting the genie back in the bottle though.
https://www.aclu.org/other/second-amendment