Corruption? Scam? I don't know which universal theory of law you are talking about, but if you are actively lying or hiding information to further your own interests then that surely could and should be illegal. You'll have to construct this theory of yours yourself though.
If you are claiming that they are acting fraudulently or acting as financial advisors and misrepresenting information... that's already a thing. If you think its a boiler room scheme - that's already illegal to.
If you are saying that someone with some stock in AAPL and would be pleased if it went up can't be a mod of /r/apple and should have criminal liability for moderating a community's activity (and would likely ban people who consistently post 'Apple is bad, buy Dell instead' or 'Avoid apple - Steve Jobs was a bad man') then you're suggesting a different thing that would be harder (in my eyes) to argue for.
