(14) You shall not insult the deaf, or place a stumbling block before the blind. You shall fear your God: I am the Eternal.
(18) Cursed be he who misdirects a blind on his way. And all the people shall say: Amen.
Josephus, Jewish Antiquities 4:276
One must point out the road to those who are ignorant of it, and not, for the pleasure of laughing oneself, impede another’s business by misleading him.
Dr. Alyssa Gray, "The Sin of Enabling Another's Sin"
"Sifra Kedoshim, parashah 2 presents one of two Tannaitic understandings of the verse: 19:14 interdicts the unethical behavior of giving someone advice or information that one knows to be untrue or potentially harmful to the advisee. Giving this untrue or possibly harmful advice is the placing of the 'stumbling block' before the hapless advisee, the 'blind.'"
(יא) ואלו עוברין בלא תעשה, המלוה, והלוה, והערב, והעדים. וחכמים אומרים, אף הסופר. עוברים משום ׳לא תתן׳ (ויקרא כה, לז), ומשום ׳בל תקח מאתו׳ (שם, לו), ומשום ׳לא תהיה לו כנשה׳ (שמות כב, כד), ומשום ׳לא תשימון עליו נשך׳ (שם), ומשום ׳ולפני עור לא תתן מכשל ויראת מאלהיך אני יי׳ (ויקרא יט, יד).
(11) And these are the people who transgress a negative commandment: the lender, the borrower, the guarantor, and the witnesses. And the Sages say: even the scribe. They transgress within the category of (Leviticus 25:37) “Do not give," and the category of (Leviticus 25:36) “Do not take from him,” and the category of (Exodus 22:24) “You shall not be to him as a creditor," and the category of “Nor shall you place upon him usury,” (ibid.) and the category of (Leviticus 19:14) “You shall not put a stumbling block before the blind, and you will fear your God, I am the Eternal."
Dr. Alyssa Gray, Ibid.
To the Mekhilta and Mishnah, 19:14 is not simply its own prohibition—as in the Sifra—but something more: if two or more persons are involved in the prohibited activity of borrowing/ lending at interest, each person, by participating in the forbidden act and thereby enabling it to go forward, sins not only by his own participation in a clearly-prohibited act, but also by becoming a means through which the other person(s) came to commit a clearly-prohibited act. Without a willing lender, there is no borrower (and vice versa); without witnesses and a guarantor, the lender will not lend; without a scribe, there is no document memorializing the loan. To the Mekhilta and Mishnah, 19:14 has become the sin of enabling others to sin (in the case of a prohibited loan-at-interest). All the parties are obligated to eschew the sin of lending at interest, and thus all are liable for enabling any of the others to advance a course of conduct that will inevitably lead to the commission of that sin. Another, more abstract way of putting it is that all the parties are part of the same normative universe, and hence all can be liable for enabling each other’s violation of this norm.
(ט) משאלת אשה לחברתה החשודה על השביעית, נפה וכברה, ורחים ותנור. אבל לא תבר ולא תטחן עמה. אשת חבר, משאלת לאשת עם הארץ, נפה וכברה, ובוררת וטוחנת ומרקדת עמה. אבל משתטיל את המים, לא תגע אצלה, שאין מחזיקין ידי עוברי עברה. וכלן לא אמרו אלא מפני דרכי שלום. ומחזיקין ידי גוים בשביעית, אבל לא ידי ישראל. ושואלין בשלומן, מפני דרכי שלום.
(9) A woman may lend to her fellow who is suspected in the matter of the Sabbatical year a sieve, a sifter, millstones and an oven. But she may not sort or grind with her. The wife of a Chaver [status marking those who scrupulously observe tithes and purity laws] may lend to the wife of an Am HaAretz [status marking those who are lax in observing tithes and purity laws] a sieve and a sifter, and may sort, grind and sift with her. But once she wets [the flour], she may not touch it, as one may not assist transgressors. And all of these were said only for the sake of peace. And we encourage the work of non-Jews in the Sabbatical year, but not that of Jews. And we inquire after their [the non-Jews] well-being, for the sake of peace.
Babylonian Talmud, Mo'ed Katan 17a
What [was the incident] of the domestic in Rabbi's house? It was one of the maidservants in
Rabbi's house that had noticed a man beating his grown-up son and said, Let that fellow be cursed! because he sinned against the words [of Holy Writ]: Put not a stumbling-block before the blind. For it is taught: ‘And put not a stumbling-block before the blind’, that text applies to one who beats his grown-up son.
Dr. Alyssa Gray, Ibid.
The more reasonable explanation is that 19:14 was introduced into these sources by the anonymous hands of editors and transmitters of these narratives in Babylonia—who had already inherited from the late Amoraic period and other stammot the conviction that 19:14 can be widely applied to a range of situations.