Pure theoretical analysis should be a simplification, which may not be appropriate. According to Keynes's theory, increasing investment can stimulate economic growth, so we can run a deficit or issue national debt in a recession, which is the same as issuing more money and lowering interest rates. But this is conditional, that is, there is no "full employment". Whether it is full employment or not, Keynes did not give the verification conditions, which is very vague. The judgment of the real society, of course, is up to the parliament or the National People's Congress to decide whether to have full employment and whether to issue additional national debt.
If we judge according to the population structure, then we can determine whether the deficit exists according to the employment expectation. When a country is in the stage of revival, the long-term trend of employment population is increasing, and the national economy is in a state of shortage, then it can temporarily deficit to increase investment and employment, economic growth will also increase rapidly, tax revenue will also increase rapidly, and the deficit is temporary. With the arrival of the employment peak, the deficit will become unnecessary, and surplus finance will be needed for export and foreign exchange reserves. Our country is at this stage.
However, after the advent of aging, the situation will change. In the case of full employment, the fiscal revenue is also sufficient, which will lead to low fiscal efficiency or high social system cost. The reduction of labor force will reduce the expectation of fiscal revenue, so surplus finance will gradually transition to balanced finance. When the labor force grows negatively, economic growth and fiscal revenue will decrease, but the cost of social system will not decrease immediately. The government also hopes to issue additional national debt to supplement tax revenue. If the decline of labor force is a long-term trend, then the significance of China's issuance of national debt can only be to reduce the deficit at the expense of the deficit and balance the finances as much as possible. America should be at this stage.
However, serious aging and domestic deficit cannot solve the problem. Only by selling the national debt to those countries with abundant labor force can the whole country be in deficit. However, strict conditions are needed. First, there are countries or regions with relatively abundant labor force in the world, which are allowed to introduce from outside; Second, the internationalization of local currency has been widely recognized. This is the goal that any developed country, including China, is striving for.
However, the world is not so ideal. Superpowers like the United States have accumulated large deficits when they don't need pension deficits. These deficits objectively promote the global investment balance and are conducive to globalization and stable economic development. But it also makes Americans take advantage.
Everyone wants to take advantage and get a deficit that exceeds the actual needs, so they can only compete or wage war by strength. Under peaceful conditions, we should try our best to balance our finances instead of deliberately surplus or deficit, but it is always the result of political and military struggles rather than the judgment of scholars. The result of competition is that there is a trend (without exception): countries with relatively rich labor force are generally surplus, while countries with insufficient labor force (including youth and aging) are generally deficit, thus achieving international or regional balance.
In a closed national economy, it is meaningless to have a deficit, because there is always a deficit, and without it, there is no currency. With the economic growth, money needs to be issued and the deficit needs to increase; When tightening, to "stimulate the economy" will also increase the deficit, but it is only a matter of increasing and decreasing. In the aging stage, the economic growth is limited, the deficit increases less, and the currency issuance is less. It looks more like reducing the deficit internally and increasing the deficit externally.