Money is not actually a real constraint on governmental spending. In other words, the government does not actually have to "tax," first, to raise the money it needs for governmental expenditures. The government spends first, essentially creating money by spending it, and then it taxes those who have money to control the inflationary effects of making so much money available in the economy.
Modern Monetary Theory assumes that we are all in this together, so our collective decisions about what expenditures we should make to achieve our common goals is always the primary question. Resources for governmental expenditures that will benefit the community overall are not what is "left over," using the taxes raised from the "private economy." Our collective economy is the main thing, not the individualistic private economy.