The Mitzvah of Eruv in Chassidic and Chabad Sources
Chabad sources treat a valid eruv as a genuine mitzvah and a protection for Shabbos. The same sources also devote close attention to the definition of reshus harabim and the conditions of a valid city enclosure.
Shulchan Aruch HaRav
The Alter Rebbe presents eruv as a protection for Shabbos and sets out the laws by which that protection is created. The four domains, reshus harabim, tzuras hapesach, walls, breaches, eruv chatzeiros, and shared rights are treated as one practical body of halacha.
Calling an eruv a mitzvah therefore carries a demand for precision. Its benefit comes from permitting what halacha allows and preventing people from stumbling where carrying remains forbidden.
Eruvin in Chabad communities
Chabad communities have maintained accepted eruvin where the local conditions and local psak allowed them. Kfar Chabad is a familiar example: its eruv belongs to its own boundaries, streets, population, and Rabbonim.
Those examples show that the discussion is not opposition to eruvin as a category. The question is whether a particular place has a valid enclosure that may be used publicly.
Each place requires its own psak
An eruv in one town does not enclose another. A walled village, an older European city, and a modern Brooklyn neighborhood may differ in every physical condition that matters.
The positive value of a valid eruv therefore cannot decide Crown Heights by itself. The Crown Heights Rabbonim examined the neighborhood question and ruled that the advertised route may not be relied upon.