GAON:
“I agree that Rav Moshe himself did not specify. However, nor do we find any statement regarding the Gezero once an Eruv has been constructed.
Hence, logic and halacha would point out that, if halachakly it is permitted to carry, it makes no sense to be able to be ‘mechadesh’ a new gezera’ to asur one from what the Torah clearly permits i.e. carrying in a reshus haYachid’.
Yes, if one would ask Rav Moshe if constructing an eruv is advisable, he would respond: although eruv has a tremendous benefits, but in this case it is better not to, due to his chashash. That is not exactly enacting a “new Gezero”. It is just leaving everything in its former status of Shav va’al Ta’se”
It does not seem so from Rav Moshe’s teshuvos. Clearly he maintained that we have to be concerned that some may think that an area does contain shishim ribo. Hence, he was concerned enough to entertain using this gezeirah against establishing an eruv in Brooklyn and Detroit. Hence, even if I agree with you, it’s difficult to argue things in Rav Moshe’s name when he didn’t say so explicitly.
In any case, if your arguing about making sense, eruvin is not one of those inyanim where sense plays a role, particularly when it comes to interpreting Rav Moshe’s shitos. Furthermore, if you are asking on Rav Moshe’s gezeirah, you can might as well ask on all of his shitos regarding eruvin, they are just as mechudash.