I recently watched a Jefferson County Intergovernmental Meeting from Feb 4th that Chuck Marohn spoke at. I work for an environmental group that addresses water pollution from sewage and stormwater and we are often calling for repair or new and improved infrastructure. During the meeting, a question came in about plans to build a sewer system in a new area of the county. It will be quite expensive and can only be done with outside state/federal assistance. Mr. Marohn comments have been used since in a debate against the project.
Mr. Marohn promoted "thickening" but I'm still baffled about how you address environmental problems caused by higher density and I wish he covered that issue more (that's my main question. Can you make any recommendations of articles and books on this issue?). After all, he showed all these old photos of his town, promoting its original complexity, but what you don't see in those images is the untreated sewage that is likely coming off those old buildings and polluting the local stream, groundwater, etc.
There are external costs to not doing something. The area where we want to build a sewage system already has areas of higher density, many old and failing septic systems, and a local stream polluted with human sewage that feeds what could be a productive shellfishing bed but can't be used due to this pollution.