DaasYochid: I checked the halochos of things done before Shabbos (siman 252) and the halocho that you mentioned-feeding grain to a mill before Shabbos, se’if 5. It is actually not as you quote it. First, the “mechaber” is “matter” it and even the Remo is leaning to allow it and only if there is a great noise “avsha milsa”,does he tend to asser (“lekatchila”). Secondly , it is only valid with a mill that belongs to a jew, not if it is a mill owed by a gentile. And the reason is obvious- when there is a lot of noise emanating from a Jewish-owned mill, there is a question of “ziluso leshabsa”_the exact words of the mishne berurah. So, on the one hand, it seems that a certain concept of “ziluso deshabbsa’ is a valid reason not to do something-but it is very circumscribed in its use, as even in the blatant case, there is plenty of reason to allow it.
I realize that,in modern times, starting with steam trains, the Poskim had difficulty explaining any issur Shabbos and hence, had to resort to rather imprecise reasons. Yet, “hovu delo losif olov”. Let us not add issurim based on flimsy reasons.