The "progressives" in the United States don't ever seem to realize that if they aren't careful, by being too dismissive of any benefits of gun ownership, they induce a lot of anxiety in people who would otherwise not be enemies.
Personally, although I enjoy plunking cans on lakes or targets at a range, and have shot a decent number of firearms, I never owned one, as I had a certain theory of my and my families personal security as to close in mortal combat derived from wrestling, judo, and jeet kune do (Bruce Lee's finishing art.)
The following analysis is based in the economic theory of externalities, which is when our actions affect others although no direct compensation changes hands.
As to a consideration that seems reasonable in a general sense, Colorado or not, one benefit of larger clip size is to make any future attempt at creating a true police state in America more difficult, as to citizens having weapons effective against para-military forces.
If that sounds an odd worry, it's naive on the flip side of that to totally dismiss the idea that any country can fail politically to the point where it becomes a contest of arms.
The Civil War, the collapse of Weimar, Republican Spain, and Allende's Chile come to mind, and one can see that if there were zero firearms in Syria, Assad woulnd't have to use helicopter gunships, or play with the idea of chemical weapons.
Of course, for those who like to push political disputes to their logical conclusion, popular verbally lately on places like O< and a dangerous sign for the Republic some would argue, if that could be optimistic about the nature of politics as rational discussion instead of the passions (see Hirshman The Passions and the Interests), the Syrian case could be read differently, as any future civil war in the United States with an armed populace would then possibly elicit more extreme measures of suppression, e.g. tactical nuclear weapons, which points to a limit to some enthusiasts of the Second Amendment.
Many who support the Second Amedment do so as a form of an ultimate veto on governmental power.
Those on the Left who only see gun violence as the consequence of the Second Amendment are therefore naive from that point of view.
On the other hand, as to the limits of the Second Amendment's efficacy in limiting governmental power, to really defeat a modern paramilitary force requires heavier weapons than one usually hears advocated being widely distributed, such as the Stinger missiles that defeated the Soviet Union in Afghanistan.
On the other hand, the partisan warfare made possible by the wide ownership of firearms in Afghanistan does point to the non-trivial protection of an armed populace as to external attack. It also of course makes for an Afghanistan that is harder to govern too, there being few unmixed blessings in life.
People on the Left have short memories on such a point, if there are other considerations as to what economists call "externalities."
Externalitites exist when there is an uncompensated interdependence. As an example, let there exist a lake with two owners, and let the reader be on one side of the lake.
Now let the owner of the lake on the other side has different aesthetic views than you, an different financial needs, and so plans to chop down all the trees and sell them for firewood, but which are trees that provide a benefit to you.
The trees are the externality, in that you benefit from their existence, but don't have to pay the other owner for their altenative use.
Now in theory, it is possible to resolve this dispute in the making by various mechanisms not involving the State, like "side payments" for the market value of the trees. That might work on a small lake, although even in that cooperation friendly environment, people have been known to get rather nasty, up to and including shooting one another, engaging in fistfights etc... .
Normally one wants externalities to be corrected as much as possible by voluntaristic action, since such corrections preserve individual freedom, something the modern Left typified on OS does not appreciate very much, perhaps right until we elect a populist Socialist who destroys the country in an alleged attempt to save it, if that is not always possible in larger environments, due to the difficulty of coordination.
Thus, many times the State is engaged in externality correction, which allows one to consider the issue of clip size from the point of view of externalities, of which there is two positive and one negative.
As to the positive externality, the existence of an armed populace makes criminals somewhat more anxious, ceteris paribus, whether or not you own a gun, since they might get shot commiting crime.
As to the other positive externality, those who would attempt to dominate and overthrow American institutions, here or abroad, have to consider the possibility of partisan warfare, in which picking off either paramilitary forces of foreign troops a la Red Dawn (we have vast resources that many in the world wouldn' mind seeing us depopulated to use, so don't dismiss that) is a consideration of some import as to the benefit of an armed populace whether or not you own a gun.
On the other hand, there is clearly a negative externality in firearms ownership, in that individuals can commit criminal acts that affect many more people than just one person, like the shooter in Colorado and the mass shooter issue in general.
As to perspective, the latter risk is not huge, if it's real too. On the other hand, every day, about 50 Americans die in traffic accidents; shall we walk everywhere?
I usually walk places, and its great for personal fitness, and an interesting way of seeing America, but factually speaking it is a minority approach to risks and rewards, and the externalities intrinsically part of travel.
But as to clip size then, the larger the clip, the greater the posistive and negative externalities.
If I have a clip of 30, I can tape them together opposed, and now have a 60 clip, and do that several times, and I am an infantryman more or less, especially with amonium nitrate and fuel oil devices; it isn't rocket science to see that.
Such a thing would make me more valuable in partisan warfare against enemies foreign or domestic, even as it also makes more danger if one was criminally inclined, suggesting that an upper bound on clip size might be reasonable, at the 15 originally used in the semi-automatic pistols in question, as well of course as background checks to identify felons and the mentally ill, even as in the latter case, the small percentage of the mentally ill who are dangerous to others in the sense of Colorado are not easy to identify beforehand.
Consider the Colorado shooter; Ph.D. candidate ironically in neuroscience: not very likely by most stereotypes.
But as to economic analysis as applied to such things, limiting clip sizes to the original design specifications might be something to consider, as it would still maintain a certain balance of power between citizenry and para-military police and/or occupying troops, plus the criminal element, just in case that former relatively unlikely contingency became something to actually care about.