Here are all SEVEN sentences from the summary:
The Second Amendment does not grant to the people the right to keep and bear arms, but merely recognizes the prior existence of that right and prohibits its infringement by Congress.
It cannot be doubted that the carrying of weapons without lawful occasion or excuse was always a crime under the common law of England and of this country.
In both countries the right to keep and bear arms has been generally restricted to the keeping and bearing of arms by the people collectively for their common defense and security.
Indeed, the very language of the Second Amendment discloses that this right has reference only to the keeping and bearing of arms by the people as members of the state militia or other similar military organization provided for by law.
The "arms" referred to in the Second Amendment are, moreover, those which ordinarily are used for military or public defense purposes, and the cases unanimously hold that weapons peculiarly adaptable to use by criminals are not within the protection of the Amendment.
The firearms referred to in the National Firearms Act, i.e., sawed-off shotguns, sawed-off rifles, and machine guns, clearly have no legitimate use in the hands of private individuals, but, on the contrary, frequently constitute the arsenal of the gangster and the desperado.
Section 11, upon which the indictment was based, places restrictions upon the transportation in interstate commerce of weapons of this character only, and clearly, therefore, constitutes no infringement of "the right of the people to keep and bear arms," as that term is used in the Second Amendment.
That is the ENTIRE Summary of Argument. The Supreme Court expects each identifiable argument to be summarized here.
Note that sentences three and four CLEARLY constitute an argument that the Second Amendment protects the right to keep and bear arms collectively for common defence and that only militia members are protected.
The transition to the second of the two prosecution's arguments is CLEARLY indicated by the use of the word "moreover" in sentence five.
If you claim that there is some context that indicates other than what I have stated, then supply the context.
The Militia references are solely to support the prosecution's argument -- that the types of weapons protected by the second amendment are only those weapons suitable for a Militia. How else is he to make his argument without referencing the Militia, or the military, or the common defense?
And only one sentence of those seven mentions a connection between the weapon and membership in a Militia. One sentence in the entire brief and you think that's an argument for Militia membership?
Taken out of context, sure, why not. In context, however, and reading the entire brief, anyone can see that the thrust of the prosecution's argument is that only Militia-type weapons are protected.