To quote from R’ Yair Hoffman’s response (in the news section) to this exact issue:
“…the Rishonim and leading Rabbis of Klal Yisroel have spoken extensively about how it wrong to cast aspersions on a minhag in Israel (See, for example, Tashbatz Vol. IV Siman 32; Rivash Siman 35, Sdei Chemed Vol. IV page 270(. It is wrong to attribute
So how and why did the custom emerge to forbid Kitniyos? The reason why kitniyos were forbidden, was on account of a protective measure. The Mishnah Berurah (O.C. 453:6, 464:5) provides a few explanations:
(1) Kitniyos are harvested and processed in the same way that chametz is. The masses would confuse the two and come to permit grains for themselves.
(2) Kitniyos can also be ground and baked, just like chametz, and people might come to permit chametz grains.
(3) The Kitniyos themselves may have actual chametz mixed in. All three reasons are therefore protective in nature. The prohibition was strictly limited to consumption; one may own and derive benefit from kitniyos on Pesach.
If such a mistake can happen, then one can easily see why some later Rishonim would push to stop a minhag that can have such disastrous consequences.
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