Imho, the global adoption of cryptocurrencies will have a devastating effect on the dollar as the dominant reserve currency and the perks that come along with it. Among the perks, according to wikipedia, is that the US and its citizens save in excess of $100 billion per year. Besides the obvious savings, the US stands to lose out in terms of political and economic supremacy, if countries start ditching the dollar to conduct trade using cryptocurrencies. Although this may seem far-fetched now, wide adoption of cryptocurrencies will make this possible. Therefore, there is every reason for the US to be afraid of cryptocurrencies and they will do everything in their power to stop the rise of it.