It is illegal to provide investment advice and sell investment products without license for a reason. This young man is exactly that reason. People are stupid and they trust other stupid people.
AFAIK, it is only illegal for a layperson to give investment advice without a license if they are doing it for compensation or if they mislead the recipient into believing you are a professional advisor. my guess is most people on wsb do not meet this criteria.
you're only liable for the advice if you meet the criteria for an investment advisor under the Investment Advisers Act of 1940, which involves actually getting paid somehow for the service. [0] I'm not an expert on the topic, but I can't see how you could possibly construe this as being intended to regulate informal discussions among laypeople. if so, why would they write the whole law around the responsibilities of investment advisors and specific criteria for being one?
similar liability exists for other people who give advice in a professional capacity (eg, lawyers, doctors, engineers), but I can't think of any situation where a layperson would be held responsible for bad advice.