It almost gets it. These positive externalities are supposed to be paid from the owners of capital, primarily via tax. This is how it very successfully worked

It almost gets it. These positive externalities are supposed to be paid from the owners of capital, primarily via tax. This is how it very successfully worked for quite some time. However, most western societies have decided in the last few decades to believe two things - 1) The government and elected representatives (and thus, voters) cannot be trusted with the allocation of capital spent on social welfare and contradictorily, 2) The government and elected representatives can be trusted with the allocation of capital when it comes to the market and the owners of capital Both of those things cannot be true at the same time.