I would suggest that KPMom's point was not that the license itself is necessary but that it is seen as evidence of a level of knowledge, skill and ability in seamanship and "mariner-ness" that the Navy has let lapse.
The Navy's core competency is fighting wars, not seamanship. A SWO is not a mariner, and his or her focus is not marine trans or nautical science. The SWO needs to have a basic level of knowledge so that he does not cause a collision or allision, and I guess nothing more or less.
The Navy disagrees with you. This was one of the key take aways from the McCain and Fitzgerald incidents.
USS FITZGERALD
The collision between Fitzgerald and Crystal was avoidable and resulted from an accumulation of smaller errors over time, ultimately resulting in a lack of adherence to sound navigational practices. Specifically, Fitzgerald's watch teams disregarded established norms of basic contact management and, more importantly, leadership failed to adhere to well-established protocols put in place to prevent collisions. In addition, the ship's triad was absent during an evolution where their experience, guidance and example would have greatly benefited the ship.
USS JOHN S. MCCAIN
The collision between John S. McCain and Alnic MC was also avoidable and resulted primarily from complacency, over-confidence and lack of procedural compliance. A major contributing factor to the collision was sub-standard level of knowledge regarding the operation of the ship control console. In particular, McCain's commanding officer disregarded recommendations from his executive officer, navigator and senior watch officer to set sea and anchor watch teams in a timely fashion to ensure the safe and effective operation of the ship. With regard to procedures, no one on the Bridge watch team, to include the commanding officer and executive officer, were properly trained on how to correctly operate the ship control console during a steering casualty.
https://www.navy.mil/submit/display.asp?story_id=103130