It is more of a theory rather than the truth you are talking about. Claiming that all ICOs are a scam is not really an accurate statement as when you look at an ANN Thread about an ICO here in the forum you will see how many support it and clearly you will see the Website and Whitepaper that comes with it. As for the US Government prohibiting its citizens it is due to the SEC of their country that makes it harder for people to invest in ICOs as they must go to the SEC first before their ICO gets approved.