In discussions of Torah, halacha, etc., people often say, "According to Chazal..." as though all the thousands of rabbis of an 800-year period spoke with one voice. But you almost never hear people say, "According to the Rishonim"; instead you hear about individual Rishonim, as in "According to Rashi..." Why is this? Why do we treat Chazal as a single entity when it obviously isn't so?
Perhaps it is for the reason that the Kesef Mishna (hilchos Mamrim 2:1) gives for why later generations cannot argue on earlier generations (see inside for specific details in this regard). His reason is that on the day that the mishna was completed everyone accepted not to argue on that which was written in it, and the same goes for the day that the talmud was completed. If so, it makes sense that we would refer to chazal as one unit, because the mishna and gemara were accepted as totally authoritative texts without exception.
It should be noted, however, that the Chazon Ish (on the Rambam there) argues on this Kesef Mishna and says that the only reason we don't argue on earlier generations is because we can't even begin to fathom their genius, so to argue on them is an excersize in futility, and he says that only Rav - the amorah - had the authority to argue on tana'im due to his unusual genius (which is really his way of asking a kashya on the Kesef Mishna, because according to the Kesef Mishna, there shouldn't be any exceptions, so why do we say רב תנא הוא ופליג, Rav is [like] a Tana and can argue). According to this Chazon Ish, one could not answer your question in the way that I did על פי the Kesef Mishna.