Yea. In the US agencies like the SEC and FTC and legal concepts such as "securities" and "accredited investors" were created to prevent exactly what's happening

Yea. In the US agencies like the SEC and FTC and legal concepts such as "securities" and "accredited investors" were created to prevent exactly what's happening with crypto- people getting scammed, or overhyped on something they don't understand. Except apparently, we have to relearn this lesson in blood every time somebody makes something slightly different but mechanically equivalent to something that's burned us in the past. You're right that it'd be hard to enforce a ban on buying/selling (although most people wouldn't do it simply because it's illegal, which would pop the bubble in and of itself). But I think banning ads, issuing public warnings, and pervasively cracking down on the clear scam ICOs would help a lot, without really impinging on peoples' freedom to shoot themselves in the foot. The nuclear option would be to rule that cryptocurrencies have no legal standing- that you can't enforce a contract around them. This would cause a swift collapse of backstabbing within the market, and the government would only be clarifying what's already true for the overwhelming majority of ICOs- they don't entitle you to anything.