"a crime isn't a crime unless you get caught".
That is precisely what this is about. Ethics is about what we instinctively know is right or wrong. It's really simple: since the rules won't (cannot feasibly) cover this, there would be no reason to be on the defensive about one's behaviour, unless of course, one knew it's unethical.
Greetings from Switzerland, David.
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„J'ai gâché vingt ans de mes plus belles années au billard. Si c'était à refaire, je recommencerais.“ – Roger Conti