One of the great case studies on how holy minhag is allowed to destroys normative halacha is bird feeding on Shabbos Shira. I'll let this great footnote from an Avi Zivotosfky article, cited by Josh@Parshablog, do the heavy lifting:
Among those who criticized this practice were the Magen Avraham (324:7); Rabbi Yaakov Emden (Siddur, Sha'ar Hagai, no. 7, p. 371 in 5664 ed.; who called the practice “foolish and prohibited”); Shulchan Aruch Harav (OC 324:8); Kitzur Shulchan Aruch 87:18; Chazon Ish (Orchat Rabbeinu, Shabbat 201, vol. 1, p. 152); Rabbi Chaim Kanievsky (Shoneh Halachot 324:12); and the Mishnah Berurah 324:31. Shemirat Shabbat Kehilchatah (27:21) is also against it, but offers a way to avoid the problem. The author suggests that one may shake out a tablecloth outdoors (in a place with an eruv), even if doing so will allow the birds to get the crumbs. However, the Maharsham (Da’at Torah 324); Aruch Hashulchan (324:3) and She’arim HaMetzuyanim BeHalachah (87:8) justify the practice of feeding the birds. Tzitz Eliezer (14:28) notes that placing food for birds on Shabbat Shirah is an old Yerushalmi custom practiced by distinguished individuals and should not be challenged. Note that despite all those who defend the Shabbat Shirah practice, no one defends feeding the fish during tashlich.See what's going on here? It is precisely the process I described in Warning. Warning. Judaism is about to become more complicated.
In the beginning, Rabbis opposed the practice of feeding birds on Shabbos Shiura. All the great names came out against it.
But when the custom refused to die out the Rabbis changed their tune.
Despite the criticism of the early achronim, later authorities began to cosign the practice. These included the
- Maharsham ( Rabbi Sholom Mordechai Schwadron who died in 1911),
- Aruch Hashulchan (a book published by Rabbi Yechiel Michel Epstein in short installments between 1884 and 1893)
- She’arim HaMetzuyanim BeHalachah (published in 1948); and
- Shemirat Shabbat Kehilchatah (written by Yehoshua Yeshaya Neuwirth who was born in 1935).
Quite tellingly an authority of our own generation, the Tzitz Eliezer, looks at sinners who openly violated rulings made by great Rabbis and pronounces them infallible. As he writes (14:28) he saw pious people feed birds on Shabbos Shira and he won't criticize them. This, in a nutshell, is how the
insane creative and original practices of one generation become the holy minhag of another.