Like I have said, there has to be some way to make determinations for practical actions of every day life. If the accepted determination is whatever the Rambam said than so be it. However, being that we are only treating them this way because there has to be some method of deciding how to treat them, it should probably be limited to areas in which a determination is absolutely necessary. However, many of the areas in which there is a certain way to treat apikorsim should not be relevant if he really thinks that he has the accurate Torah Hashkafa. (I don’t know the person who is the subject of this thread so I don’t know whether that is the case here, but I am speaking in general terms.) Therefore I would be hesitant to openly mock such people, which is not to say that I wouldn’t express disagreement.
But my main purpose here is the second discussion.