There are to kinds of needs :
- Continuous needs
- Ponctual needs
Continuous needs typically benefit from the ask for one stack
Ponctual needs typically are a pain when one stack is ordered, because you end up with too many items you have to send back to the logistic network.
The problem is : for a "continuous need stack", all you have to do is set and forget. It's not a problem if the initial quantity is one, and you have to set it manually to one stack, because once it is set, you never touch it again.
On the opposite, ponctual needs are always ponctual, you order for what you want, and if default behaviour is "order for a certain quantity", you have no choice but get that quantity as soon as you select the item, and then cope with sending stuff back. Every single time.
The benefit/drawback balance of this "order xxx many upon item selection" is clearly not beneficial.
All this comes from the fact that the order for delivery is sent to your robots as soon as you choose a item type. Nothing in real life works this way. Before you start to be delivered, you always have time to tell how much you want before. Imagine you're on an online store, you want to buy yourself a SSD, as soon as you choose the ssd type, the bell rings, and you have a truck with 1000 ssd in a box. And then you take one, and send back the 999 others because you never wanted them.

If there is no way to delay the delivery until you have time to sepcify how much you want of something, then the default quantity should be 0, in order to let you decide how much you want before delivering you.