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The question is a little too poorly presented to be of much practical value. There are sometimes wide gulfs of difference between “laws”, “regulations” and “ethics”. The things barely have nodding acquaintance with each other sometimes.
When I see people acting “unethically” in public, and I do see that from time to time: nurses and doctors talking disrespectfully about patients outside of the office, for example, and even naming those patients (or at least describing them to each other so that others can deduce who is being talked about), then I generally just file it as “how not to act”, and “what practice to avoid”. (If I were familiar with the person being talked about, then I might make a quiet recommendation to seek service elsewhere, and I may or may not say why.)
Where I work now – since a recent takeover of our company by a huge multinational industrial conglomerate – ethics and compliance to law, local regulation and “good behavior” in general is stressed above all else. We’ve had numerous online training sessions to expound on exactly the kinds of “good behavior” that are expected – and one of those expectations is to remove ourselves from the presence of those who are engaging in various forms of likely, apparent or obvious bad business practices. One of the things we’re being told to do is to not only remove ourselves, but to say why we’re doing that, so that if minutes are kept or if the others present are ever interviewed – and presuming they will tell the truth at that point – it will be on record that we said we were leaving for a particular reason (the bad conduct or unethical business that might be discussed in our absence), and that we did, in fact, leave the meeting or whatever was going on.
I’ll be interested to see how this plays out in practice. I’ve never been involved in “shady dealings” except that one time back in band camp, but I doubt that things are ever as cut-and-dried as presented in training scenarios.
As for people swimming in posted No Swimming areas, I might mention the restriction to the people if I knew more about the circumstances: if the beach was closed for safety reasons and they didn’t know that, or if they couldn’t read or simply hadn’t seen the sign, they might appreciate knowing. As for people swimming in a “drinking water reservoir”, I’d totally let that go. Enough cosmic dust falls from space on that reservoir every single day of the year to outweigh the effect of anything that a few human swimmers would do, even if they peed while they were swimming.