I am not learned on this are but here is my own opinion:
Erev Rav are Jews who knowingly and purposely do actions against the Torah to harm the Jewish People.
Korach and Datan in the Bible were examples of the Erev Rav.
Erev Rav does not include Rabbis who do things within the possible framework of the Torah with good intentions even if they are wrong or end up being proven wrong. These are just Rabbis who did the wrong thing and may have sinned but they are not Erev Rav since they did not knowingly and purposely try to undermine the Torah and do harm to the Jewish Nation. Erev Rav does not include those who try to do what is correct but do the wrong thing and don't learn from their actions but remain fools. These are stupid fools who have sinned but they are not Erev Rav.
I say that Reform and conservative Rabbis are Erev Rav.
Korach Datan weren't Jews? Were they literally Erev Rav that left Egypt with The Jews or were they just self-hating Jews?
No they werent Egyptians. In Sefer Shemot you may remember Moshe telling a man "Rasha Lama Take Reecha". I think a perush says that he was talking to Datan and Aviram.
