Are they banned to do this?
or are American companies not allowed to raise money for their projects via ICO?
Companies can raise funds by ICO. Only accredited investors worth over 1 million dollars who are U.S. citizens or residents may purchase ICOs. Regular people are not allowed as the SEC has declared them unregistered securities. To protect you from yourself, your government has banned you from participating.
But, is this banning people from the USA to invest in some ICOs and then spend their online/digital cryptocurrencies in the digital world? If someone will ever exchange it for fiat money, it will be tracked but before that, it is not possible and he can do it, or not?
Otherwise, if such cryptocurrencies are banned in the USA, why some big guys like CoinBase are allowing people from the USA to trade with Bitcoin and other altcoins?
So you mean, if a company from the USA wants to raise funds via ICO, it is allowed, but is not allowed to accept regular normal people to invest in their ICO? They only can accept participants from Europe or other countries where it is allowed