Freighters are special. Standard freighters may be built on any Populated or Major Planet, and do not require Crew Units or Dilithium (they use industrially produced Dilithium crystals not suitable for starships). Specialized freighters must be built on a Major Planet, but are still exempt from Crew and Dilithium requirements. There are plenty of hopeful freighter captains and crews currently without a ship.3 Boarding Parties assigned to freighters are still subtracted from your Marines treasury. Of course a freighter may always be built in any unit which may build a warship, except for specialized docks.