Let's see now, shall we? "He, she, or they" . . . Well that eliminates the old, tired and errant 'right of the militia' theory quite nicely, now doesn't it? That is, unless you are aware of female militia members back in 1740 or 1819. But even if that were the case. There's another law posted on the linked page that grinds any [lame and fallacious] argument into powder.
Then there's this little quote from Blackstone, (that the author used on the title page):
"Misera est servitus, ubi jus est vagum, aut incognitum."
["Wretched is the thraldom where the law is either uncertain or unknown."--William Blackstone: Article 1, Section 8, Clause 16, Commentaries 1:401--4]