It is clearly stated as I posted in my last post:
I understood your previous post perfectly well.
I also understand both the guidance that you quoted and the reason for that guidance very well. The guidance is addressing uncontrolled or minimally controlled foreign areas where terrorists may strike American military and naval personnel simply because they are in uniform. The prupose of not wearing one's uniform in such situations is to avoid provocation of an attack.
Cruise ships have exceptional security. The cruise lines now require submission of immigration information in advance so they can submit it to government authorities for screening, and anybody who fails the screening receives a full refund for the cancellation of the affectedbooking. There's also very tight security on the piers and in the harbors where each cruise ship calls and phenomenal security -- including a team that's trained and equipped to deal with any attempted infiltration by a team of terrorists -- aboard each cruise ship itself. It would be exceptionally difficult for terrorists to penetrate that security. As a result, a cruise ship at sea is one of the safest environments in the world. If you can't wear a military uniform aboard a cruise ship, you better not wear it off base at all. It's also important to remember that formal evenings take place when ships are well out to sea, so there's no danger of being observed in uniform from land.
If the question had been about wearing one's uniform to or from the cruise ship, or about wearing one's uniform ashore during a port of call, I would counsel against doing so -- and most especially so in a foreign port. These are the very situations to which your guidance about not wearing the uniform in foreign places absolutely does apply.