This is my understanding of what MMT has to say about this topic. The old classical view of economics (and the most libertarian) maintains that government revenue constrains (or should do) the capacity of governments to spend. This view assumes that the State issues a commodity currency, whether it's sea shells, gold/silver or a gold/silver backed currency. The State's capacity to issue currency is limited by its revenue, that is, its ability to access and hoard whatever commodity it issues as legal tender. Governments have various means by which to access and hoard commodity currencies. They can tax, they can wage war, they can debase the currency or they can nationalise the means of production of these commodities. These are what can be referred to as government revenue streams. Since we threw off the last remnants of a gold backed currency AND floated the AUD, the Australian government, like every other sovereign nation in the world now finds itself in a position where its revenue does not constrain its capacity to spend. Sovereign nations now have a never ending supply of money at their disposal. The function of taxation therefore is not for revenue raising, it is simply a means by which the State can impose its currency on the people and control the amount of money in the system ie add or withdraw purchasing power from the private sector. When it spends it adds purchasing power, when it taxes it subtracts it. And the key metric for determining whether and how much money the State should inject or extract into the system is the employment rate. This is the background of how our modern monetary system now works. Government funding is limitless. It is an eternal well that can never dry and the taxpayer now or in the future is not required to pay for any of it because governments don't need taxpayers to fund their activities in the first place.