I see, so the conversation you want to have is that I am automatically wrong ("But that conversation will go nowhere if you think you have a constitutional right to a high-capacity magazine"), you are automatically neutral (because you are open mined about the destructiveness of a plastic box) but everything is framed in terms of need and enjoyment. I see.
So you don't have a right to post on the internet for all to see. You don't have a right to email because it allows you to communicate with lots of people with little cost. I don't see the 1A says that speech to large numbers of people is part of the right any more than you see a right to a box. And when you invariably say "But it's guns and they are killy and only meant to kill" realize speech kills. A lot. A turd in FL burned a Koran and 20 UN workers in Afghanistan were slaughtered. Yeah, the syria thing was BS but the one in Afghanistan wasn't. People lie routinely in political campaigns. Bush II got elected and then waged war based on a pack of lies. How many people dies because those lied allowed the people to support his stupidity?
An arm is easily defined and frankly that you would think that nukes falls under that or even entertain that is telling. An arm is that which a soldier can bear by themselves for their defense. An RPG is an offensive arm. Not a defensive arm. It's real simple actually. A rifle is a defensive arm in that it is suited for that. A single RPG pull of the trigger can kill tens of people. A single pull of the rifle trigger kills at most one. Offensive v. defensive. It's done.
You don't want a conversation. You want a conversion by me to your deluded way of thinking that objects are responsible for the havoc their operators cause. We don't ban cars because people kill with them. We don't ban kitchen knives because more people are killed by those than assault weapons. Hell, more people are killed by hammers than assault weapons. Look it up. FBI stats. Google it as many articles have been written on it.