The government is powered by belief too. When a critical mass of people start saying "This is not my government, and I'm not subject to its authority", it ceases to be the government. This last happened (unsuccessfully) in the U.S. in 1861, but is a regular occurrence in many other parts of the world.
The effect of 2009's QE was to couple the full faith & credit of the financial system with the full faith & credit of the government, effectively backstopping the financial industry with the trust that the government had built up over 230 years. This worked, but it was not free. The cost was an erosion of that trust in government, which you see in movements like Occupy Wall Street, the Tea Party, Black Lives Matter, the alt-right, Trump, sovereign citizens, and Democratic Socialism.
As long as things are good, the government (and the financial system) can continue to build up that trust that they spent down in the financial crisis, and we'll have weathered the storm with no problems. Things are still not good for many people. And so the risk is that if there is another crisis in the next few years, while that trust is depleted, the whole society will come crashing down, like Syria or Venezuela. Not just a financial crisis, but a political crisis as well, because the two of them are now coupled in peoples' minds.