My simple opinion, as a defender of 2A.
The purpose of the 2A was to give the citizenry a chance to overthrow a hostile/despot government. Secondarily, it was intended to give individuals the chance to defend themselves against stronger individuals (no individual 'might makes right'), as well as more simple things such as home defense and hunting for food. To maintain the intent of the 2A, it necessitates that all individuals have access to the same arms, and that those arms are identical to what the military is capable of deploying. I do not know how to normalize this with things such as nerve agents, napalm, cruise missiles, and of course, nuclear weaponry. If one cannot accept things such as that in the hands of citizenry, then I think semi-automatic, reliable, easily manufactured, assembled, and capable of firing a widely available round which can reliably kill one or more humans is probably the middle ground. To disarm the populace is to welcome an authoritarian regime. One must be willing to accept the deaths of innocents due to certain individuals deciding to kill a bunch of people in order to maintain the ability to enact the intent of the 2A. Basically, the tree of liberty must be watered with the blood of innocents, far more often than the blood of tyrants.
To give some rationality to the above, I personally consider authoritarian regimes the number 1 existential crisis of the current era. Number 2 being climate change. Number 3 is a distant third, and I'd have to think on what I gave a shit enough to consider to be an existential crisis... I dunno, loss of all bees or something.
I accept that most people do not think the same way I do, and I respect anyone's opinion that the above is absolutely retarded.