"That is all well and good, but where would you ever get ten million residents from, and where will you find a hundred Mecha Regiments? In case you had forgotten, a hundred thousand trained pilots are more than most nations could boast, and you plan to put them all on one ship. One very large ship.
Not to mention the cost and complexity of actually building such a thing and the four hundred Cutters you will need to staff to deploy the ship's defensive force. Or the millions of support staff to keep the whole thing running. Are you going to depopulate a colony somewhere?" Major Miller's rant predictably focused on the logistics of the matter, but he had a point.
You couldn't just make millions of people appear and join your Company. There simply weren't enough Reavers for the purpose, and most of them had already been claimed.