Eruvin in Earlier Chabad Sources and Communities
Earlier Chabad sources include both the positive mitzvah of a valid eruv and exacting halachos governing city streets and enclosures.
The Alter Rebbe: mitzvah and exact halacha
Shulchan Aruch HaRav presents a valid eruv as a communal mitzvah and a protection from hotza'ah. The same se'ifim define the four domains, reshus harabim, shishim ribo, tzuras hapesach, walls, openings, eruv chatzeiros, and the limits of each device.
The positive value of eruv is therefore inseparable from validity. A structure that does not meet those halachos cannot be defended simply by pointing to the mitzvah of establishing one.
Eruvin in the time of the Rebbe Rashab
Eruvin existed in Russian towns and cities during the period of the Rebbe Rashab. Those places could have walls, gates, limited road networks, and populations very different from a modern American metropolis.
Their history shows Chabad communities using eruvin where halacha and local conditions allowed. It does not make the walls or streets of one Russian city into a precedent that automatically encloses Brooklyn.
The same halachos applied to changing cities
Chabad sources do not offer a policy slogan for or against every eruv. They require Rabbonim to apply enduring halachos to the city that actually stands before them.
That is why population growth, new roads, demolished walls, and public access matter. A route accepted in an earlier period may require a new psak after the city changes.