We've devolved into an academic discussion here but it's fun so to continue... Navy ships carry Coast Guard law enforcement detachments whenever they're conducting law enforcement operations anywhere in the world specifically because Posse Comitatus prohibits Navy and Marine personnel from engaging in law enforcement (the Coast Guard is statutorily tasked with law enforcement). This is a massive pain in the ass, we wouldn't do it if your definition of PC was the legally accepted interpretation. If 5,000 miles away from the nearest land (or 50 feet of Puerto Rico, in some cases since a lot of those patrols are conducted in that area) is considered subject to PC, then certainly Puerto Rico is! Again, believe me, I've sat through numerous classes on this, it was part of my profession (I was a military officer). Certainly you could form a tortured logic chain a la the Bush administration on torture that would allow for it, but it's certainly not the currently accepted view of the law and it would take more than the gradual decline into oblivion of PR to cause an about face on that interpretation. Not to mention, as I stated previously you'd be doing a huge disservice to the Marines to set them up for failure in a task that they're neither trained or equipped for.
Certainly what you say is true from the military's point of view. I don't question that one bit. But in the end it isn't the military who decides these matters. (well maybe in the very end it is!)
Remember Eisenhower (who likely had similar briefing on Posse as you) sent Federal troops into Little Rock! And Arkansas is not even a territory, it's a State!
By the way I believe PC is a very very good idea with respect to internal, i.e., domestic affairs, but I think any argument that PC applies outside the United States is bound to fail. It is clear from my reading of the law that PC doesn't apply to territories of the United States that are not States, despite the military's chosen interpretation of the law. We may get a chance within the next few years to see if I am wrong.
Speaking of executive orders: (1987) At the federal penitentiary in
Atlanta, a group of the Cuban refugees mounted an uprising. When federal agents could not control the riot, Reagan waived the Posse Comitatus Act and ordered a unit of Delta Force operators to subdue the uprising. (found on the net)
Here is another opinion found on the internet with regard to the 2011 Defense Authorization Act: The NDAA places the American military at the disposal of the President for the apprehension, arrest, and detention of those suspected of posing a danger to the homeland (whether inside or outside the borders of the United States and whether the suspect be a citizen or foreigner). The endowment of such a power to the President by the Congress is nothing less than a de facto legislative repeal of the Posse Comitatus Act of 1878, the law forbidding the use of the military in domestic law enforcement.
the PC Act has been interpreted, except apparently by the military on a very selective basis, as not applying to territories.
The many precedents make it crystal clear to me that were the Puerto Rican Police and National Guard not able to put down a riot in Puerto Rico, they won't be, that US troops would be sent without so much as batting an eye.
I am not concerned about this, but I am gravely concerned about the ease with which PC has been brushed aside by the executive in he case of "Domestic" disturbances.