When the question of building an eruv came up in Detroit, local shliach R. Yankel Krantz a”h consulted with the Rebbe. The Rebbe told him to oppose its construction since it would cause negligence in Shabbos observance and rejected the argument that it would save those who carry.
Reb Leibel Schapiro relates:
As a Shliach in Detroit MI, Reb Yankel Krantz a”h became involved in Rabbonus work. When a discussion came up at the Vaad Horabbonim of Detroit about whether to put up an eruv, Reb Yankel consulted the Rebbe about what stance to take.
“Oppose the construction of an eruv,” the Rebbe told him unequivocally, “because it will cause negligence in Shabbos observance.”
“In the past,” the Rebbe explained, “large cities had eruvin, but those days were different. People were not so mobile, hence there was no room for worry. These days, however, with people moving from one place to another, someone who is used to carrying in a place with an eruv may accidentally carry in an eruv-less city due to habit.”
The Rebbe then addressed the argument that it may still be worth making an eruv to save those who carry anyway from chilul Shabbos. This should be done in secret, the Rebbe said, so that both advantages are gained: the public is saved from transgression, and at the same time, they don’t pick up on risky conduct.
“Indeed, this approach was suggested when the discussion of erecting an eruv in Manhattan arose. And whether this was followed, I am not telling you…”
(Shlichus Kehilchoso Miluim p. 14)
From The Weekly Farbrengen by Merkaz Anash