(This letter was sent by way of Mesora to Judaism.com - currently selling Red Bendels under the claim it forms Jewish tradition. Rabbi Zucker has responded denying this view, referencing the Rishonic authorities)
I read with great fear and anxiety your response to The Jewish Times regarding the issue of the sale of red threads as a protective amulet. The reason that I say "fear and anxiety" is that your letter seems to say that as long as there are opinions in print supporting a certain practice, that practice may be encouraged even if it runs contrary to towering Jewish authorities and texts. It is as if to suggest that while authorities such as the Tanna'im, the Radak, and the Rambam may clearly prohibit in very strong terms the wearing of red threads, as long as two rabbis (who lived within the past hundred years and are recognized to be illustrious) say that it is all right, then there is no problem. I beg of you, as someone who undoubtedly has the interest of fellow Jews in his heart, to please reconsider your position. I appeal to your tzelem elokim in this request, based upon the following sources:
The Rashba, alluded to in the Be'er Moshe that you quoted, (presumably in Teshuvos HaRashba, volume 2, letter 268) states, "There are customs that the women observed on their own, and it is prohibited to violate (those customs) provided that they were observed based upon a correct issue..." (There follows a list of customs observed by women as cited in Yerushalmi Pesachim, some of which are deemed appropriate, and others which are not). To use this as a basis to say that since women established the custom of tying red threads, therefore it should be accepted, seems to be a distortion of the Rashba's explicit words.
But more...the Tosefta in Shabbos 7:1 explicitly states that wearing a red thread is a clear violation of a Torah principle, darkei ha-emori. With that in mind, please see the commentary of the Radak on Yeshayahu 40:21, where he states, "...people thought that many things and certain actions would help or damage, sicken or heal. These things are not based upon wisdom or medicine or natural forces, but rather they are based upon the repeated customs of people throughout the generations...and these are the darkei ha-emori." Does not the "ancient custom" of the red thread fit exactly into what the Radak derides?
And worse...please see the Rambam's Moreh HaNevuchim 3:37, wherein he states unequivocally that the engagement by people of practices that constitute darkei ha-emori in order to protect themselves from danger will not only be ineffective, but on the contrary, will result in new dangers brought to them as a result of their sin.
If this is not enough to convince you, my dear brother, I beg that you at least consider putting something along the following lines on your website when offering the red threads for sale:
"The use of these threads that are for sale was mentioned by the Tanna'im as being a violation of Torah law. The Radak and the Rambam clearly reiterate the sin involved in using them, and the Rambam in particular says that using them will bring about further calamity in your life. There are, however, two rabbis who recently wrote that there is no problem with using these threads since their origin is based upon the established custom of numerous common, lay people in earlier generations."
At least in this way, you are practicing full disclosure and informing the people of both sides of the issue, along with the risks that they may be taking in choosing a particular side.
I invite you to join me in a continuing full study of the issue, to pursue our divine mission of avodash HaShem through chochmah, so that we may clearly and properly understand what it is that HaShem has designed for us. I hope that you accept these words in the true spirit in which they are written and sent, with ahavas Yisroel, and with the hope that with the true path of Torah and mitzvos, and without the need of any external, tempting illusions, we may all merit to see bi'as goel tzedek bimhayrah veyameinu.
Rabbi Saul Zucker