In large part *because* of all the gun violence, there are lots of other people that a good law-abiding person might someday need to massacre, such as a criminal, or an intruder, or a school shooter, or maybe a fleeing shoplifter, or the U.S. government.
ESPECIALLY the U.S. government.
Ask a gun defender, they’ll tell you: they might need guns to massacre the U.S. government someday.
They'll tell you if you *don't* ask.