Q. See question 2004 above. Why shouldn’t everyone have the blue wool techeiles-thread added to their tzitzis, since there is no downside and there is nothing to lose if one uses it out of doubt?
A. As mentioned in the prior question, Teshuvos Vehanhogos (O.H. 1: 26), maintains that one who wears techeiles, where it is not commonly used may transgress on the prohibition of “Lo Sissgodedu” or creating division and separation in the community.
He further adds that one may be also be violating the proscription of “baal tossif” or adding to a mitzva parts that do not belong to it.
In addition Shulchan Aruch (O.H. 9: 5), rules that medakdekim or careful people wear strings of the same color as the garment. Rema (ibid.) asserts that Ashkenazim use only white Tzitzis even on colored taaleisim.
As mentioned above Horav Shlomo Miller’s Shlit’a opinion is similar to the above, and to avoid wearing the available “techeiles” in our days, since it is a counterfeit product. (Maayanei Shlomo O.H. 1-3). The Rov adds that Ben Yehoyada (Bava Metzia 61) asserts that the Sittra Achra and powers of impurity have a foothold on the imitation k’lo ilan marketed in our times and there is a strong Cabbala k’peida or impediment on using it.
Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit’a