The sages of Israel say: By day the sun travels below the heaven, and by night above the heaven. The sages of the nations of the world say: By day the sun travels below the heaven, and by night below the earth. Rebbi said: Their words seem more logical than ours, since by day springs are cool, and by night [they are] warm. (Pesachim 94b)
In recent years there has been a debate, most publicly regarding R' Natan Slifkin's books, regarding what degree of scientific knowledge was possessed by the ancient Jewish sages. We see from the above quote that Chazal themselves did not think they possessed the perfect scientific knowledge that some people nowadays credit them with. Rebbi, the author of the mishna, rejected the scientific opinion of the Jewish sages (חכמי ישראל) because the scientific evidence seemed to be against it.
Why do the charedim insist on holding a position about Chazal that is against the above gemara, as well as against common sense?
Perhaps the answer is as follows. The "Chazal knew science" school is often associated with belief in "daas torah", or the infallibility of the greatest modern rabbis. It seems to me that saying Chazal erred about science is a threat to the belief in daas torah. If Chazal could err, then so can modern rabbis, who are clearly not as great as Chazal. And if modern rabbis can err, then statements of theirs may be rejected if not accompanied by a sufficiently persuasive justification. For the charedim, at least, that is unacceptable. Due to the perceived social need for daas torah, they are forced into a corner when it comes to discussing Chazal's knowledge as well.