Square, I apologize for hurting your feelings.
Life is about learning.
It hit me hard to learn that zionism was a sham when i was 16, too; a large part of my Jewish identity was based on nationalism, and when i saw rav avigdor miller trash it it was very, very difficult.
Rabbi aryeh kaplan is not getting into the minutiae of every category of emunah in his well written and important books, but this is included in the belief in Torah shebaal peh, in the truth of all that chazal passed down, and in the understandings of what Torah is and how its masters were endowed in its infinite knowledge. He also was writing for people who are not frum and had no education – he had a lot bigger issues to teach than these finer points of the parameters of torah shebaal peh.
As it happens, he was not some sort of gadol hador or posek either, and he made some mistakes of his own, including accepting evolution on some level, when chazal clearly say that every part of creation was made as is, and did not develop. But he was a very holy person and had a tremendous amount of positive influence and Yiras Shomayim, so this is a side issue.
I don’t know where you came from, or who your teachers were, and i too would praise someone for amassing Torah knowledge – this is a finer point, which is, however, important, and discussed in poskim.
Chief among them in achronim is the aruch hashulchan. Not a chassidishe sefer or an obscure shailos veteshuvos sefer – one of the main sources for halacha in klal yisroel. And he says it outright that it is completely forbidden to believe that chazal erred in science issues.
This idea is in the gra, rav yonasan eybeshuts, maharal, maharsha…in rishonim it’s in the rashba, and the parts where chazal darshen pesukim – that would certainly be considered disbelief in drashos, “machchish magideah” in the lashon of the rambam, one who disbelieves in drashos chazal.
Of course, we’re not commander to be fools. We’re supposed to investigate and understand chazal, and we’re not necessarily supposed to ignore empirical scientific fact – the maharal and others routinely reconciled chazal with science…you never see achronim or rishonim just say that they were wrong.
the rebbe of the sefardi pachad yitzchak reprimanded the author severely for suggesting that chazal had erred in their understanding of lice not reproducing – and he was trying to be more machmir, and say rhat we shouldn’t be allowed to kill them because “now” we know that spontaneous generation – something chazal never even talked about, is not true. His rebbe sternly told him he was wrong, and he accepted.
Again, I’m sorry for the news coming as such a surprise. Feel free to read “torah, chazal and science” for a very clear, lengthy and well sourced position on the issue in its entirety.