The issue of kitniyot. The term meant pulses and beans in the Talmud, but now extends to include peas, certain other vegetables, peanuts, and any new food that reaches the market. It seems strange, just typical of the excessive, casuistic preoccupation with minutiae that now dominates Orthodox Jewish life and seems to have absolutely nothing whatsoever to do with one's relationship with God. Can there possibly be a case for the defense?
The basic code of Jewish Law, the Shulchan Aruch itself, makes no mention of any ban on kitniyot. But the commentary on it of Rav Moshe Isserles (the Rema, 1520-1572) which is the accepted norm of Ashkenazi Jews, says that it has become the custom in Ashkenaz to be strict and not to eat kitniyot on Pesach. Sephardi Jews know no such ban.
The idea of the Biblical ban on chametz during Pesach itself is strange. Dough can rise, ferment. The ban on seems rooted in the idea that puffery, whether of grain or humans, is an unnatural state. Mystically, chametz is negativity. We need to be reminded occasionally to recognize the dangers of arrogance and to try to exclude it from our lives if we want to thrive and succeed spiritually.
But kitniyot do not "rise". Two reasons are given for the custom. In Europe pulses were often stored with grains and taking some out of the sack or barrel on Pesach might lead one to eat forbidden produce by mistake. And in wet climates pulses sprout. This was seen as giving the appearance of chametz.
Regardless of the reason, by the sixteenth century the whole of the Ashkenazi world banned kitniyot on Pesach. The Sephardi world did not. But even strict Ashkenazis agreed that food cooked with kitniyot did not make one's vessels chametz on Pesach, and one could eat on utensils in a Sephardi house where everyone else ate kitniyot. There is absolutely no logic for banning kitniyot, other than an error of botanical understanding, or dereliction of care, that is confined exclusively to Ashkenazi brains.
The accepted principal is that where a custom has spread universally, or throughout a specific community, it becomes the equivalent of law and is retained even where the original reason has fallen away. This is the force of "custom". Offending against custom may not be as serious as offending against a Biblical law, but the fact is no rabbinic authority of any status will agree that any widespread custom no longer applies.
Why do logically anachronistic or paradoxical customs never disappear? In part, it is simply the "nature" of the Orthodox/Charedi rabbinate nowadays. They will happily add all sorts of excessive strictnesses, even when the Shulchan Aruch is lenient, but will never ever dream of making life easier or saying a custom no longer applies!!! All religion nowadays gives the impression of being more concerned with social conformity and belonging than anything spiritual or commonsensical. And people who live in closed or defined religious societies are too fearful of social pressure (perhaps my child won't get into the right school or might not get a suitable "shidduch") to dream of not doing what everyone else is.
The fact is that human beings are inconsistent, irrational, credulous, and superstitious, and are consumed with the need to conform and the desire to show off. Humans do really stupid things and think they are important. They salute flags, they put their hands on their hearts and swear allegiance, they sing banal songs in praise of their homelands or leaders, they wear silly little tokens in their lapels, ridiculous, pointless relics of bygone ages, such as neckties, kerchiefs, unnecessary buttons and buckles, and the most ridiculous felt and beribboned things on their heads, for no logic reason other than to conform or show off. They say pointless things and meaningless words such as "seeya", "hi", "I mean", "like", "don't yer know", and "say what". Why? Just because others do. And in a religious context we use words like "amen" and "halleluyah" that we could dispense with and lose nothing of sense or communicative value. We are trained in some countries to eat with knives and forks and hold them in very specific ways. (One of the biggest culture shocks Europeans encounter in the USA is that hardly anyone knows how to hold a knife and fork properly.) Does all this matter? No, not really, because they are all little ways of signifying belonging to a group, a class, a culture, and we do it as reinforcement of where we want to be or with whom we want to be seen identifying with.
So much of all of human life is based on earlier cultures, social conventions and yes, even mistakes. What matters surely is not the origin but the usage. Are these strange habits beneficial? Can they add to the quality of our life, making it more meaningful and significant? I believe they do. They force us to stand back and question difference, to break or contrast patterns of behavior and to bring the spiritual into the mundane. Simply to think about what one eats is important. And if one has a yearlong habit of relating to food one way, I see nothing wrong in upping the ante over Pesach so that we try that bit harder to think about what we are doing. That, in the end, is the purpose of halacha of whatever degree of strictness. Nice moral theories and values are useless unless translated into everyday action. Ritual does not guarantee. Nothing can, because of our human nature. But I believe it helps.
Orthodoxy is such a minority interest, such a strange way of conducting one's life, that we aficionados like to make a virtue of our craziness. We find value in almost everything. Precisely because kitniyot and similar eccentricities make no sense in the rational world, observing the rule on Pesach is a way doing something for a purely religious reason. As Tertullian said, "Credo Quia Absurdum Est." I believe it precisely because it is absurd. Our variation is that we do it despite its seeming absurd. That is what is meant by the Biblical term "Chok". It is a spiritual sacrifice of reason to raise our awareness of another way of looking at life.