So what they really meant was impracticable.
Your comment just demonstrates you don't actually understand how economies of scale work. The reason things get cheaper the more you make and sell is because of all the costs that go into producing an item that aren't directly involved in the manufacturing process as well as costly aspects of the manufacturing process that 3D printing eliminates. First we have design. 3D printing doesn't affect this at all, however it is one of the costs that is reduced per item in an economy of scale. Which means 3D printing does scale and invalidates your argument right off the bat. Second we have the manufacturing process. This usually involves specialized equipment, like molds for plastic components or custom robotics for assembly. Producing that equipment is a cost that must be recouped with the sale of the item. The more items you produce and sell, the more the cost can be distributed. 3D printing eliminates this cost. Instead we just have one general piece of manufacturing equipment which can be distributed among the entire manufacturing community. Third, there's the cost of human labor which is significantly reduced by 3D printing. Finally, there's the costs of defects. If there's a 10% chance of an item being defective, producing 10 means one will be defective on average and the cost of that one item can be distributed in the sale price of the other 9. But if you only produce one and that one is defective you must produce a second one that now costs twice as much in order to recoup the cost of the defective one instead of 10/9ths the price. So, 3D printing does scale, but not as much as ordinary manufacturing, but that's OK because it is cheaper than ordinary manufacturing even at scale.
While it might seem extreme to compare drones and nuclear weapons (and let's face it, it probably is), within a limited scope they are actually the same. Of course, so is every other weapon ever invented. There are lots of differences between nuclear weapons and drones. The number of people they kill in a single strike, difficulty and cost of construction, availability of raw materials, risk to civilians. But here's where they are the same. They give a huge advantage to a side who has them against a side that doesn't. The problem is that it's unlikely to remain one-sided for long. The question we have to ask ourselves is if having a temporary advantage now followed by a world where our enemies have drones is worth it. The same could have been said for firearms, automatic firearms, submarines and fighter jets. Ultimately, should we develop international laws to govern how these new weapons can be used? Absolutely, if the current laws don't already provide the necessary restrictions. But, unless we suddenly live in a world where the need for a military is no longer necessary, I don't see haw we can not develop any weapon which gives us an advantage over our enemies and reduces the risk to our own soldiers.