@djc with positive externalities, it’s not problematic to scale the benefit with the value. (although of course the public wants some surplus too, we shouldn’t pass as benefits the full value of the positive externalities if the provider of the externalities doesn’t require that. parents often do enjoy their kids!) so all else equal, the generosity of the maximum benefit we should be willing to provide (though again, we might provide less) should depend on the net value of the externality. 3/