If they're not minimally profitable in some general sense, such that the benefits of building and maintaining them are not at least paid by the benefit of using

If they're not minimally profitable in some general sense, such that the benefits of building and maintaining them are not at least paid by the benefit of using them then no, they shouldn't be built. Unfortunately, when you factor in the externalities of carbon emissions, loss of habitat, and other biosphere stressors (the biosphere being the life support system for all life, including humans, and which we do not have the means to replace), then most human activity in living memory cannot pay for itself. This is sad, but we can't fix it until we acknowledge it. We're using up our life support system when we build a highway or airliner, not investing in anything.