It's perfectly true that the system is perfectly capable of running alone without any external stimulus applies. The economy will keep being the economy no matter how much you tamper with it. The main problem people have with that is not that the economy won't "work", it's that the economy working necessarily means things like heavy business cycles, cyclical unemployment, a general tendency of wealth to move upwards, and a relatively fast accumulation to the level where those who have accumulated wealth begin to have serious power over politics and will impose meddling with the economy for their benefit.
It will work fine, it working just isn't what humans generally want to happen.
The idea that your wealth ought to grow exponentially regardless of whether the economy itself is growing and how much you contributed to the economy is ridiculous. What did people expect from this arrangement other than accumulation of wealth at the top?
By the way, the economy won't work, it will collapse at some point, because 3% growth over two thousand years would imply colonizing entire galaxies. People think they have a birthright to eternal 3% growth without even being aware of what it means to grow exponentially for that long.
