> SEC rules, etc. apply to all civilians whether or not you're engaged in SEC-related activity.
There are professional rules that do not apply to non-professionals, including SEC rules. For example, lawyers can't give advice in many situations - their free speech is curtailed. Doctors and other healthcare professionals, in some places, are excluded from the 'good Samaritan' exception to injuring someone (i.e., if you find someone injured and try to help, and accidentally cause more harm, you can't be prosecuted).
> There are professional rules that do not apply to non-professionals, including SEC rules. For example, lawyers can't give advice in many situations
For giving legal advice, that's mostly backwards (in most US jurisdictions); its generally illegal for anyone other than a licensed lawyer to do what is legally considered giving legal advice (this is one of many things that constitutes unauthorized practice of law), whereas for a lawyer they are allowed to within certain ethical bounds.
You have observed a pattern of behavior on HN, and conjectured a plausible legal framework that explains that behavior.
That's great. But, as is going to be the case probably more than 99% of the time that you try to infer the law from how people behave on HN, the rule you seemed to have inferred ("anyone except a lawyer is free to give legal advice in any situation, but lawyers are more restricted") is very much not the actual legal rule.
i suspect part of the error is that your conjecture about the rule implicitly assumed that both lawyer's and non-lawyer's behaviors reflected the same degree of knowledge of, and concern for adhering to, the applicable legal rules.
Whatever your theory, non-lawyers are free to give legal, medical, etc. advice as long as they don't present themselves as qualified professionals or, in many cases, charge for it.
Professionals in the field are restricted in the advice they give.
False. It applies “In time of declared war or a contingency operation” to civilians “serving with or accompanying an armed force in the field”, 10 USC § 802(a)(10). This was one of several “gap-filling” changes to US federal law adopted to address problems with effectively holding contractors and others associated with the military accountable for crimes overseas in the '00s (among the others was the Military Extraterritorial Jurisdiction Act of 2000, which extended federal civilian criminal jurisdiction over certain offenses committed outside the United States that did not previously have extraterritorial application, when the offender was either a civilian accompanying the US military in certain capacities or a former military member subject to the UCMJ at the time of the act but not at the time of prosecution.)
UCMJ doesn't apply to any civilian. SEC rules, etc. apply to all civilians whether or not you're engaged in SEC-related activity.