I would suggest you read the Second Ammendment and the United States vs Miller opinion. These are "militia" arms by definition and everyone is in the militia. These rifles are used for target shooting, pr4actical shooting, national match shooting and just taking out to the range for a day of fun. Yes they can be used for varmint shooting but their primary use is to be held by the people of the United States of America to keep politicians in line. If politicians should decide to completely engage in tyranny then the realization that there are several million of these rifles out there (or similar rifles etc.) will give them pause because the benefit of their tyranical rule will probably be outweighed by the cost of trying to impose it.
It has a great deal of similarity to the Fleet in Being concept of naval warfare. The simple existence of an enemy fleet one may well be able to defeat ties down assets that might otherwise be employed.
The mere presence of 100 million "assault" and scoped deer rifles stays the hands of our most rabid anti-freedom statists.