Many cities might not have been able to afford more powerful guns for their police without the discounts provided through trade-ins.
Well, by this logic, does not the selling of the "old" police weaponry keep the criminals who purportedly buy these weapons behind the curve, thus doing the cops and society some benefit (in addiditon to the funding potential of the weapon sales? Don't want to support the Chinese government do we?
Mmmmm...pistol whip....