I think most people here can tell the difference between someone who is in the military and who is not. As you just explained yourself, you fit the bill of someone that is in or used to be in the military, as I believe you might have said at one time you were in the military.
So if you know yourself you might somewhat fit that bill and you are visiting Okinawa and know that this is going on, and further know that any MP or OSI type as well as any E-7 and above can ask to see someones ID, why not comply and get on with your life? I think most of the people who have so much of a problem with it are not currently in Okinawa. If you thought about what the problems would lead to if you did not show your ID, the whole island has their eyes on us and takes pictures randomly of service members (especially on gate 2 street), do you think refusing to show an ID and whatever problem this may cause would be seen as that in the media?
The only thing that would be reported is that an American (probably military, because the media is not going to differentiate you from anything else) refused to show an ID and that this patrol is not working. All of this would further cause problems, that are not needed at this time, giving more ammunition to the news channels here. I cant understand why people are so apprehensive about this, if your not military, get over yourself and show your passport or residency card.
Of course we all know that the patrols have no authority over local national civilians, but they do have authority to ask for an ID card of someone who might fit the description of a military member (somewhat in shape, clean cut, not with a full mountain man beard, etc.). I am pretty sure this has the backing of the JP's and the government as we MP's are not allowed to even respond off base without first notifying the JP's and a translator tagging along, so I am sure these patrols have been "blessed", as the courtesy patrols who patrol gate 2, have an understanding of what they can and cannot do while off base, through what the JP's tell us and we brief to those patrolling