I and others use our phones at several community pools, but photos are not taken as a courtesy. ..A watch is a much smaller and less common/recognizable device as a camera... a phone is a universally recognized recording device.
I've distilled your rebuttal to these points, as they are the ones I believe we are going to disagree over.
Essentially, your comments imply that a person is on their guard around a mobile phone, because it's known as a universal recording device. Yet, there are numerous examples of this not being case. The infamous Mitt Romney "47 Percent" speech was one such example where clearly someone was surreptitiously videotaping something with a phone. So clearly phones can be concealed, such that nobody noticed or cared. In my own experience I have on occasion unlocked my phone to check it while in the locker room, and discovered the last app I had opened was the camera, made painfully apparent by viewing a naked guy changing in front of me. He never even looked in my direction, which suggests to me that phones have become so commonplace people don't really think much about people checking them everywhere. Add to the fact that in such a situation, it's usually pretty obvious that someone is taking a picture with their phone since they are pointing it at the subject, holding it steady and using awkward arm positions to do it.
I would argue the same principle applies to the watch. ESPECIALLY a FaceTime camera, which will be mounted on the face of the watch. Whether or not people aren't paying attention to a wrist watch in the same way as they might a phone, In order to take a picture of someone, the face of a watch will have to be awkwardly pointed at the subject in such a way as to draw attention, in a very un-watch like fashion. Add to the fact, the screen will be showing the image the camera sees, something especially unusual with the typically black-faced Watch; and the photographer will have no way to align the photo except to strangely peer over the top of the watch, combined with using two hands in order to press the button to take the picture. If someone is standing in their underwear close enough to be effectively photographed by a smartwatch camera, and they don't notice this out of place behavior, then frankly they deserve to have their photos plastered on the internet.
As you said yourself someone could just as easily hide a camera inside a hat, and the same goes for that. If someone is strangely standing near, much less pointing their hat in the direction of someone who is stripping, I would hope somebody would be taking notice of such odd behavior.
In any event, there is no more reason to ban a FaceTime equipped watch from a location that already permits phones. As the Watch becomes more popular, and camera equipped watches become as common as phones, (especially considering the watch is but one radio away from replacing the phone in many respects), then to the extent people acknowledge a camera is a recording device, so will they too knowledge any watch may be as well.
In the interim, banning smartwatches will likely happen wherever they ban phones -- the taping of a live television show for instance comes to mind. And for places that have polices of no photo taking, like your pool, or movie theater, then the same will apply to a smartwatch. And anyone caught breaking the rules will be penalized. As I pointed out, it's just as easy to surreptitiously take a photo of someone on a phone, pretending to check messages, but it's not likely to go on consistently without someone being caught -- in the act or after the fact. And what would happen if one of these swimming pool photos ended up on Facebook? Probably a ban on all phones at the pool, no? The same is true for the watch. The person in the theater awkwardly holding up their phone or watch to get a good recording of the movie will get prosecuted.
Ultimately, I would expect the ability to take a selfie with a watch, or answer a FaceTime call will outweigh any potential privacy concerns, especially given the realities of such photography efforts being rather overt. But then clearly this is where we disagree. Only time will tell I suppose.