As a bochur a friend of mine who learned in the yeshiva of Rav Chaim Kreiswerth ZTL in Eretz Yisrael (Mercaz Hatorah) asked him if he can carry in the yerushalyim eruv.

The Rov responded ” I personally know the Rav who supervises the eruv.  I know he is a very big talmid chochom.   Therefore, I’m telling you not to carry! Because he is such a big talmid chochom he knows to use many many kulos and i dont think you should rely on those kulos.”

(Explanation:  Considering all the challenges in construction of an eruv, the bigger the eruv is and the more varied its terrain, the harder it is to build it. So, it is very difficult to build a very big eruv. In order to save klal yisrael from being michshol the builders of large eruvin will rely on many leniencies. Not because they themselves are lenient Rabbis, but rather because they are Rabbis that care enough about klal yisrael that they will do the utmost to save klal yisrael from carrying, even if it means using kulos which are not conventionally accepted as the main opinion.  Thus a G-d fearing Jew will not want to use such kulos,  but a Rabbi with yiras shamayim will build it for those who are unaware.)