Rabbi Avraham Chaim Bloomenstiel commenting on Another Kind Of "Blood Libel":
There is a tale told of two fellows locked in a machlokes. Eventually, they agreed to go to the Rabbi for resolution. The first party carefully outlined his side of the argument. The rabbi listened intently and concluded, “My son, you are right.” The other party then outlined his appraisal of things, to which the Rabbi replied: “You are right, too.” The rabbi’s wife, who had overheard the conversations with both men, said to her husband, “Rabbi, you told them both that they were right. They can’t both be right!” To which the rabbi replied, “Hmmm… you are right too!”
Everything written in Chabakuk Elisha’s post is 100% correct and is emes. But, everything in the article upon which Chabakuk Elisa has come to comment is true as well.
The article that touched a nerve for Chabakuk Elishsa is from an online repository of summaries of shailos and teshuvos. Its points are basically two:
1. The article brings an interpretation from Rav Chaim Kanievsky explaining why there is a custom/chumra of some not to accept blood transfused from a non-Jew.
2. Rav Kanievsky was apparently cautious to note that this minhag should not be treated as a minhag shel shtus.
Chabakuk Elisha, if I am reading him correctly, believes that:
1. The source for the custom/chumra at issue is not really valid.
2. The real source is bias and bigotry against non-Jews.
The operative assumption of R’ Kanievsky’s interpretation is that there may be, note “may be,” inherent physiological differences between Jews and non-Jews that may, again “may,” have ramifications in the halachic sphere. This point is not without basis. However, these differences are more tied to the dietary metzius (reality) of non-Jews rather than to some inherent bio-structural difference.
Niddah 34b and Shabbos 86b bring a discussion regarding the zera of a Yisroel that is within the body of a Nochris and whether or not it is tuma if poleit within 3 days. One proposed answer hinges on the idea that the body temperature of Jews differs from that of non-Jews. While the original question is unresolved, the possibility that there may be physiological differences between Jews and non-Jews is left open. Note one of the main reasons proposed for possibly variant body temperatures is the difference in diet; non-Jews eat things that Jews do not eat.
These Gemoras combined with others in Shas (i.e. Avoda Zara 31b) strengthened the possibility of differing biologies enough for the Chasam Sofer to base a ruling upon it. In his Teshuvos Y.D. 175 the Chasam Sofer rules that medical statistics or findings based on a non-Jewish majority should not be considered definite for Jews because the possibility may exist that the physiologies are incomparable. However, in a case of life and death the Chasam Sofer says that we may rely on these findings and consider them definite because of the leniencies associated with pikuach nefesh and the principle of lo halchu be-pikuach nefesh achar ha-rov, “in matters of life and death, statistical majorities/minorities are not always relied upon as they would be in a normal situation.” Parenthetically, we should note that there are many contemporary poskim who doubt the applicability of the Chasam Sofer’s ruling in the modern medical world. 
Another place where this possible difference bears halachic import is in the case of a non-Jewish wet nurse. It is interesting that, again, the diet of the non-Jew seems to be a big part of the issue.
YD 81:7 the Mechaber paskens that, while a Non-Jewish wet nurse may nurse a Jewish baby, the practice should be discouraged because her (the wet nurse’s) diet is not kosher. In a similar vein, the Rama adds that a Jewish woman who must eat non-kosher food for health reasons should not nurse her child because the non-kosher food will harm the baby. The source for this idea that the diet of the non-Jew is the main issue, not the nature of the non-Jew herself, is the Rashba on Yevamos 114. The Rashba holds that a woman’s milk is not inherently treif; rather, its status depends upon her diet. The Vilna Gaon proposes a source for this Rashba from the well-known Medrash in Parshas Shemos. The Torah states that the Egyptians brought a wet nurse from the Jews to feed Moshe. Rashi explains that Moshe refused nursing from an Egyptian woman because he was going to be a navi and could not, therefore, eat non-kosher food. Based upon this proof, we see that the issue is not the non-Jew herself, rather the simple fact of circumstance that she ingests tarfus.
Either way, the possibility of Jewish biology differing from non-Jewish biology is not strong enough to bear weight as a psak, but it is enough to substantiate certain personal chumras, for example, not wanting a blood transfusion from a non-Jew.
Why is this not a minhag shel shtus?
While the technical and colloquial usages of “minhag shel shtus” have become very blurred, there is a workable definition. Basically, this is a custom which cannot be tied to a source in Shas Bavli, Yerushalmi, or any of the classic works of Kabbalo.
Under this definition, we find many accepted practices, particularly among the Ashkenazim, which could receive the label. In fact, some did. In the original edition of the Shulchan Aruch , Simon 605  was bluntly entitled: Minhag Kapparos be-Erev Yom Kippur Minhag Shel Shtus Hu, “The Custom of Kapporos on the Eve of the Day of Atonement is a Foolish Custom.” 
The title was changed to its modern form sometime in the 1570’s when the Ashkenazi editions incorporating the Rama were first printed.
The reason for the Mechaber’s treatment was that the minhag of kapparos has no Talmudic source.  Rather, its earliest mention is a Rashi to Shabbos 81b.
Nevertheless, the custom has taken root due to the approvals of the Rosh , Tur  , and Mordechai.  Amongst Sephardim, the custom has gained popularity because the Ari was known to have embraced it. 
Another candidate is kitniyos. Rabbeinu Yerucham flatly called it a minhag shel shtus.  No less a sage than Rav Yaakov Emden concurred that the minhag was problematic and declared it a mitzvah to annul the whole thing.  We hold onto it today due to its wide acceptance and the Maharil’s passionate defense of the custom. 
In contrast, we have some customs which may appear foolish but are not. For example, see Orach Chayim 442:6 that records the minhag of some persons to scrape down walls and chairs that may have come in contact with chometz. The Mishneh Berurah warns that we should not think this is a minhag shel shtus. Why? Because it has a basis it can be tied to in the Yerushalmi.
In conclusion, those who want to be machmir about not receiving a blood transfusion from a non-Jew have what to rely upon. However, the sources may only be enough to warrant a personal custom/chumra and not a hanhaga for an entire community. Also, Rav Kanievsky’s defense of this custom as “not a minhag shel shtus” is warranted; we see that the possibility of differing biological traits does exist. Additionally, we know that it is not preferable for an infant to nurse from a non-Jew due to the fact that she eats tarfus. Perhaps this reasoning carries to blood transfusions as well? Again – not enough for a psak, but enough for someone to be machmir if they want to be.
I just don’t see anything in the original article that warrants the “annoyance, anger, and disgust” expressed by Chabakuk Elisha. While it is true that non-Jews and Jews are different (spiritually and, according to some, perhaps even physically), it is also true that we have a responsibility to uphold and exercise the tenets of basic human dignity. I just don’t see how the Revach article poses any contradiction to either of these two facts.
Anyone who wishes to comment on this post or Chabakuk Elisha’s post, please read (or re-read) the original article found here.
 Heard from Rav Ovadia Yosef, shlita. Rav Yosef also writes about this topic in his teshuvos, but I cannot lay my hands on the source at the moment.
 For an example, see edition published Venice, 1565.
 According to Sheilos u-Teshuvos Shemesh Tzedaka O. C. 23 the simon titles in early editions may not have been written by the Mechaber or, alternatively, the original titles were liberally edited. Nevertheless, R’ Karo still opposes kapparos strongly in his Beis Yosef.
 The Beis Yosef goes further bringing the Rashba who views this practice as darkei ha-emori.
 Yoma 8:23
 O.C. 605
 Introductory notes to Yoma.
 Magen Avraham 605:1. See Kaf ha-Chayim 605:8, Shu”t Yechave Da’as II:71, and Ben Ish Chai: Vayeilech 2 for more information about the Sephardic adoption of this custom.
 Toldos Adam ve-Chava IV:3.
 Mor u-Ketzia 453
 Maharil 187.