The conclusion is inescapable that these weapons were deliberately injected into Iraq by the US government, almost certainly with the expectation that they would wind up "in the wrong hands".

Let's look at my reasoning.

One of the first things every soldier learns, from second one of his/her service, is that weapons are never, f'g never left unsecured and never, ever unaccounted for.  Losing a weapons card - a form the size of a business card upon which is entered your assigned weapon's model and serial number, arms room inventory/control number (a locally-generated number assigning it a particular space in the arms rack), and your personal information - is as bad as losing a weapon.

Most vets can still tell you the serial number of their weapon.  

In a military unit, someone losing control and accountability of a weapon stops everything until control and accountability of the weapon is reestablished (and the responsible parties suitably chastised).  My unit used to inventory weapons a minimum of twice a day when in the field, and before leaving any location for another.  If the accounting came up less than perfect - everything stopped until the problem was rectified.

Examples I've seen (or been directly aware of):

• A bayonet fell out of a scabbard in a training area.  An entire company spent the better part of a day low-crawling the ground looking for it, until it was found.  (This was a good reason, in peacetime, why most units left their bayonets in the footlocker in the arms room.  One more thing to lose....)
  
• An amphibious vehicle swamped and sank during an engineer unit's river-crossing exercise, with the crew of 5 or 6 going into the water.  Three or four of them became separated from their rifles while swimming, and a night vision device sank with the vehicle.  The vehicle was recovered in a day or so, but the rifles were not found.  That company spent the next month guarding that stretch of river 24/7 while the unit brought in a crane and tried to make a dredge from the crane and some of its float bridge.  They were unsuccessful, but the weapons were never written off, and their spaces in the weapons racks in the arms room, never filled.
  
• After the Vietnam war, many, many M16 rifles were captured by the North Vietnamese, and put into the international arms market (in one way or another).  By the serial numbers, the US was able to know the weapons' provenance (and sometimes recover them from circulation).

How nice for the neocons. We may as well get used to 60 to 80 KIA/day. The oil must flow.