I don't think it's illegal for citizens, more like it's illegal for icos to sell to US citizens who not accredited investors.
https://www.sec.gov/news/press-release/2017-131"The Report confirms that issuers of distributed ledger or blockchain technology-based securities must register offers and sales of such securities unless a valid exemption applies.
Those participating in unregistered offerings also may be liable for violations of the securities laws"Bloody hell. Thanks for sharing that link.
Here's a quote from the full SEC text found at:
https://www.sec.gov/litigation/investreport/34-81207.pdfMoreover, those who participate in an unregistered offer and sale of securities not subject
to a valid exemption are liable for violating Section 5. See, e.g., Murphy, 626 F.2d at 650-51
([T]hose who ha[ve] a necessary role in the transaction are held liable as participants.) (citing
SEC v. North Am. Research & Dev. Corp., 424 F.2d 63, 81 (2d Cir. 1970); SEC v. Culpepper,
270 F.2d 241, 247 (2d Cir. 1959); SEC v. International Chem. Dev. Corp., 469 F.2d 20, 28 (10th
Cir. 1972); Pennaluna & Co. v. SEC, 410 F.2d 861, 864 n.1, 868 (9th Cir. 1969)); SEC v.
Softpoint, Inc., 958 F. Supp 846, 859-60 (S.D.N.Y. 1997) (The prohibitions of Section 5
sweep[] broadly to encompass any person who participates in the offer or sale of an
unregistered, non-exempt security.); SEC v. Chinese Consol. Benevolent Assn., 120 F.2d 738,
740-41 (2d Cir. 1941) (defendant violated Section 5(a) because it engaged in selling
unregistered securities issued by a third party when it solicited offers to buy the securities for
value).