That type of gun was used to devastating effect in the trenches of WW I, to force German soldiers to abandon those trenches, and subject themselves to even more withering firepower when outside the trenches.
Well, maybe not wrong. The Court noted that there was no evidence to show that short barreled shoguns were militia weapons, since no one showed up to represent Miller that day.
Again, the court did NOT say that Miller was not entitled to own one, they said that without satisfactory evidence presented - in a court of law by a witness subject to cross-examination or a certifiable document subject to inspection by both sides of the case - that it WAS militarily useful, they couldn’t simply say on their own authority that it was militarily useful and thus that Miller was entitled to own one.