DY: how could the Gra argue on the rambam? And rambam was a Chacham and he was niftar 800 years ago- ergo chazal.
The term Chaza’l is used for chachomim until chasimas hagemora, i.e. Tannaim and Amoraim. The reason the Gr’a argues on the Ramba’m, even though it’s quite unusual for an acharon to argue on a rishon, is probably because he felt that writings of the Ramba’m which were influenced by outside sources have no special reason to be accepted.
L’olam va’ed certainly doesn’t apply to say, cholov yisroel
Can you please explain? I have a feeling that you might be misunderstanding the reason for those who are matir.