There are many components that make something a place. Institutions, People, and Architecure are three big ones. Major loss of any of those categories would contribute to the place feeling hollow, as if the place is gone and all that remains is the geography and its name on a map.
For Boston, the People component is threatened, as the housing crisis has caused and continues to cause many Boston-area natives to move further and further out of the core. Obviously, this needs to be addressed by building more. But, do we really need to sacrifice the Architecure component in order to do so? These "museums" of iconic rowhouses are part of what make Boston a place worth caring about and living in, just like its People do.
Plus, rowhouses on narrow streets aren't just cute--they're a very efficient way to house people. They also lend themselves to pleasant neighborhoods where people are encouraged to walk instead of drive cars which need parking, the true enemy of density. There is still plenty of parking, single-storey retail, and even (god forbid) triple-deckers that could be demolished and rebuilt as mid- or high-rises before we need to go after already-dense neighborhoods of 4-5 storey rowhouses.
