[burlesona]

Yes, but, the actual math matters. There are a lot of banal public infrastructure projects that cost much more than the value they create, and there are also theoretically productive public investments that are double-dipping into the same “surplus value.” To illustrate there are many roads that were built in hopes of spurring development and development never occurred, but the roads are maintained anyway at a substantial loss of taxes. And to make a simple hypothetical as you did, suppose the train subsidy creates some surplus, but then the city also runs a bus and a ferry and installs bike lanes all on the same route and all of these are gloriously uncrowded… at this point we’ve probably eaten up all the surplus value and then some.

This is hopefully obvious, and yet the excess road building problem is ubiquitous in the US and costing us fortunes.[1]

So we can’t just hand-wave and suggest that all infrastructure and all subsidies always create more value than they cost, we have to be critical and especially careful not to pretend that non-financial benefits can pay for real financial costs.

1: https://youtu.be/7IsMeKl-Sv0