1) FOLLOWING THE MAJORITY OPINION IN MATTERS OF "PIKU'ACH NEFESH"
QUESTION: The Gemara quotes a Beraisa which says that one should not desecrate Shabbos or Yom Kippur for a sick person based on the opinion of women or Kusim, "but they join to another opinion" ("Aval Mitztarfin l'Da'as Acheres"). RASHI explains that this means that if two men say that the sick person needs to eat and three men argue that he does not, a woman may not join the two men who rule leniently and thereby balance the opinions so that the sick person may eat (because of "Safek Nefashos l'Hakel). One should not feed the sick person in such a case because the majority opinion (of men) says that he does not need to eat.
Rashi's explanation is difficult to understand. The Gemara earlier (83a) says that in matters of Piku'ach Nefesh, the number of opinions is irrelevant ("Ein Holchin Achar Rov De'os"). As long as there are two people who say that a sick person must eat, he may eat for the sake of Piku'ach Nefesh regardless of how many people say he does not need to eat. Why, then, does Rashi here say that a sick person may not eat when two men (and one woman) say that he needs to eat and three men say that he does not? A sick person may eat whenever two men say that he needs to eat.
(a) RASHI apparently understands that according to the Gemara's conclusion (in the name of Mar bar Rav Ashi, on 83a), the Gemara does not accept the logic against following the majority opinion in matters of Piku'ach Nefesh. Rather, one should follow the majority opinion even in matters of Piku'ach Nefesh (ROSH 8:13). This is also the view of the SHE'ILTOS.
(b) In contrast, the RAMBAM, RAMBAN, and ROSH (8:13) maintain that the Gemara concludes that one should not follow the majority opinion unless the minority opinion is that of only one person. The Rosh therefore explains that the Gemara here must refer to a situation in which a woman supports the view of one doctor who says that the sick person must eat (but not two doctors, because two do not need support).
(c) The Rosh cites the RIVA who challenges the entire notion of not relying on a woman. After all, why should a medical expert who is a woman be less reliable that an expert who is a man? Rather, the Riva suggests that the word "Lo" must be inserted into the text of the Gemara so that it reads: "v'Ein Omrin Lo Ye'asu Devarim Halalu..." -- "We do not say that these things may not be done based upon the opinion of women... but rather we accept theirs as a second opinion." That is, one should feed a sick person based on the opinion of women, even if they contradict the opinion of the men ("Mitztarfin l'Da'as Acheres").
(d) The RIF (as cited and elucidated by the Rosh) seems to have had a similar Girsa, except that his text of the Gemara concluded, "Mipnei she'Mitztarfin l'Da'as Acheres." According to his Girsa, the Gemara says that one should not accept the opinion of women who say not to desecrate Shabbos, "because they are of another mind." That is, even if women insist that refraining from food will not endanger the sick person's life, their opinion is not accepted. They are suspected of having a tendency to be extra stringent in observing the Mitzvos even at the risk of a person's life, like the approach of the Minim who reject Torah she'Ba'al Peh which teaches that one may transgress most prohibitions in order to save a life.