Why is forex illegal in USA?

Could you please clarify why trading in foreign exchange, or forex, is considered illegal in the United States? I've heard differing opinions and am curious to understand the legal framework behind this. Is it due to regulatory concerns, potential for money laundering, or some other reason? Could you also elaborate on any specific laws or regulations that prohibit or restrict forex trading within the US? Additionally, are there any exemptions or loopholes that traders can utilize to engage in legal forex trading?