DY,
“If he is unaware of the Rambam (etc.), he’s guilty of am haaratzus”
Note, Rav Chaim Brisker’s rule that when it comes to the 13 Ikrim the Rambam’s shitah is :
“Nebech An Apikoras iz OIch An Apikoras” !
i.e. you can not claim “Am Haaratzos” when dealing with Yud Gimel Ikrim. (He brings proof from various Rambam’s.) Thus, it needs to be assessed if it falls into the above category.