No Line.
Excerpts from this thread--
http://www.thehighroad.org/showthread.php?t=76377&highlight=line+drawn
If the purpose of the 2A is to protect "the security of a free State" or
The 2A has NOTHING to do with hunting OR target shooting. It has to do with protecting a free republic against the rise of tyranny. It has to do with patriots being well armed enough to threaten to kill dictators and their henchmen before they can take power. Period.
as Travis McGee said (
http://www.thehighroad.org/showthread.php?s=&threadid=75974 ),
... THEN ...
Certainly anything useful for personal defense is also useful for state defense. But there are weapons that are arguably not particularly useful for personal defense which are essential for state defense.
If we care about "state defense" as much or more than personal defense - and remembr it was emphasized in the 2A as a justification for - then the line should be drawn not at the weapons useful for only personal defense, but to include the weapons suited for state defense.
Q1. If a man is walking down the street pointing a rifle at each person he passes, do you have to wait until he shoots someone to stop him, using force?
A1. Obviously: No. His actions actively put others in immediate danger of death or great bodily injury.
Q2. If I live on a 10,000 acre ranch in the middle of the high plains, and I want to have 2000lb bombs in my barn, shouldn't I be able to?
A2. I think yes - those bombs are not putting anyone else in danger besides maybe myself, and the principle of freedom should prevail.
These two cases illustrate the distinction between drawing a line in the sand for all circumstances - a line specific to weapons - and working off the principle that a person should be free to do what he wants as long as he doesn't hurt someone else, or put them in immediate danger.
We shouldn't say that "The cost to society for X is too high in all circumstances". This is innaccurate because all circumstances are not equal. To make an analogy, it would be like saying nobody should be able to go over 65 mph on a private racetrack because too many people drive drunk on the freeway.
Furthermore, "the cost to society" is not defined. What is the cost in relation to? Who is the cost imposed on? How are the benefits taken into account? This leads to a utilitarian conclusion which guarantees no individual rights.
Instead, we should start with the principle of freedom and then ask, "Does allowing X in this specific circumstance put anybody in immediate danger?"
Following this criteria, no weapons are proscribed out of hand. Note that all small arms and most crew served weapons fall into the "does not pose immediate danger to others" category, even if stored in my suburban garage. WMD's would definitely fall into the "danger" category if stored incorrectly. Please note that we currently allow private corporations to have all manner of deadly chemicals and biological agents, but only if they can ensure they are safely handled and stored.
I don't know how to state it any more clearly than this: You are free to do whatever you want as long as it doesn't hurt others or put them in direct immediate danger. This goes for weapons, propane, driving, burning leaves - whatever.
For example, as others have mentioned, the propane tank in my backyard is a huge energy store. If it were to explode, it would surely harm my neighbors. However, as long as the propane is contained in a properly designed container and left alone, it is safe. Thus, it is allowed. However, if I were to start a bonfire under the tank, that action is directly putting my neighbors in immediate danger and they have legitimate cause to use force to stop me and put out the fire.
I went on to discuss small arms. All small arms are mechanically inert and require significant operations to discharge. Regardless of how destructive the projectile (automatic grenade launchers included), they do not just "go off." Thus, they are allowed since I can store it in my garage and it poses no more threat than the propane tank in my backyard. However, if I were to put a bunch of monkeys in the garage with the loaded grenade launcher, I've now created a direct threat to my neighbors and they can stop me.
Hopefully these additional examples help understanding. One of my points it that there ought not be a "line in the sand", as we normally put it. We should follow the general principle named in my first paragraph.