If Bitcoin becomes widespread enough that most people hold their savings in it, then it will greatly and permanently reduce liquidity in the financial system, lead to a decrease consumer spending and cause major ructions in the global economy.
If bitcoin could have pose a danger to the economy by the way of its increasing in adoption rate to what we are having today, then we would have sensed this right from time as it continues to advance, but to the greatest surprise, there is nothing to fear or risk on with bitcoin adoption in the world economy system than to create several opportunity and our most desired privacy and security in which we wanted with the profitability in it.