The marginal factory has an expected net present value of zero - if it were positive, market forces would already be adding them. Maybe you can find some exampl

The marginal factory has an expected net present value of zero - if it were positive, market forces would already be adding them. Maybe you can find some examples of over-regulated long-lived infrastructure (nuclear power comes to mind), or non-excludable goods (roads and bridges), but there's a remaining problem that these things don't typically live long enough for a 30 year old to build and then enjoy the fruits thereof in their 80s.