It's not an argument from authority. It's the same as saying that you can surmise that a racecar driver probably likes racecars. I spend my free time running a gun forum...and you can likely surmise that I like guns.While I am not an Admin on a gun forum (solid use of argument from authority), I do happen to know that the constitution says "shall not be infringed". But, hey, the guys that wrote that weren't Admins on a gun forum. Maybe we can run our rights by you before we choose to utilize any rights given to us by someone that is not an admin on a gun forum.
If we want to be really specific, which it seems you do, the constitution doesn't state "shall not be infringed." What you are quoting is an amendment to the constitution that was ratified two years later.
We can agree to disagree on the following, but I believe that some limits are appropriate. I don't want rappers living in Baton Rouge or any of the gangs across the US to have easy access to RPGs. I don't want Elon Musk, Mark Zuckerberg, or Mark Cuban buying and possessing nukes. That is an "infringement" on "keeping and bearing Arms," which I assert is acceptable.