What they fear is Ponzi pyramid schemes damaging the economy. Several ICOs have reached a billion USD without any product and often anonymously. These can bankrupt whole areas of a country. Now is the time to stop them.
Remember that their growth is exponential and one at a billion already puts it high in the history of Ponzi schemes (Ponzi himself 'only' caused around 200 millions. Madoff is the recordman with between 50 to 150 billions). Let them grow for more generations and there is a very big risk even for national economies.