That is a highly flawed argument. Your local law enforcement has light and medium tactical gun trucks, some have armored personnel carriers, and I bet there's a couple with tanks.
===================================
The two key phrases in the 2nd Amendment are "militia" and "keep and bear" with the word "bear" being a key word with a definite definition in the scope of the Amendment.
My larger point is this: if law enforcement has "light medium tactical gun trucks, some have armored personnel carriers, and I bet there's a couple with tanks"...
then the citizens must be allowed to own those as well (even though, none of that can be carried individually (i.e. bear)).
"Also, back in these days, what was the most destructive type of arms? Cannon. Guess who owned most of he cannon? Not the government - it was private companies that had cannon on their ships"
Who is keeping the arms in that case? private companies (keep), and the ships are, in a way, "bear"ing (or carrying) the arms, not individuals.
While individual citizens may indeed be capable of "keeping" such arms, they most certainly are not able to "bear" them per the definition in the Heller case as well as the known definition from the 18th century forward.
District of Columbia v. Heller
At the time of the founding, as now, to “bear” meant to “carry.” See Johnson 161; Webster; T. Sheridan, A Complete Dictionary of the English Language (1796); 2 Oxford English Dictionary 20 (2d ed. 1989) (hereinafter Oxford).https://www.supremecourt.gov/opinions/07pdf/07-290.pdf...
We think that JUSTICE GINSBURG accurately captured the natural meaning of “bear arms.” Although the phrase implies that the carrying of the weapon is for the purpose of “offensive or defensive action,” it in no way connotes participation in a structured military organization. From our review of founding-era sources, we conclude that this natural meaning was also the meaning that “bear arms” had in the 18th century. In numerous instances, “bear arms” was unambiguously used to refer to the carrying of weapons outside of an organized militia. The most prominent examples are those most relevant to the Second Amendment: Nine state constitutional provisions written in the 18th century or the first two decades of the 19th, which enshrined a right of citizens to “bear arms in defense of themselves and the state” or “bear arms in defense of himself and the state.”8 It is clear from those formulations that “bear arms” did not refer only to carrying a weapon in an organized military unit.
To Bear - to carry, or support or hold up.
Dictionarium Britannicum: Or a More Compleat Universal Etymological English Dictionary Than Any Extant 1730
https://books.google.com/books?id=CoRZAAAAcAAJ&pg=PP95#v=onepage&q=bear&f=false
To Bear - to carry, to hold up
An universal etymological English dictionary, comprehending the derivations of the generality of words in the English tongue 1742
https://archive.org/stream/universaletymol00bail#page/100/mode/2up/search/bear
To Bear - to convey or carry
A dictionary of the English language. 1792
https://books.google.com/books?id=j-UIAAAAQAAJ&q=to+bear#v=snippet&q=to%20bear&f=false
Bear - to support, to carry, to wear
Webster's Dictionary 1828
http://webstersdictionary1828.com/Dictionary/bear.
The 2nd Amendment does in fact have limitations...to what an individual can carry (among other limitations like age).
Now, if any law enforcement is "allowed" to have a main battle tank at their disposal...the citizens must be allowed to own them as well (even though they can NOT bear them) because the point of the 2nd amendment being an "equalizer" on the government.
The "military," is a totally different entity which contains a lot of weaponry that a citizen could never bear and therefore has no bearing within the scope of the 2nd Amendment.