A Muslim who does not know the Quran can think he's a Muslim, and can think that Jihad is not part of Islam, and thus walk around as one of your "moderate" Muslims.
But what happens when an Imam finally gets around to telling him what the Quran demands of Muslims? He will then have a choice between becoming a "real" Muslim, or deciding that Islam is not for him (at which point he would be considered an apostate by Muslims who actually read the Quran and Hadith, and thus subject to the death penalty).
Or he/she can choose to believe that the quran is full of stories & what went on at the time of Mohammed doesn’t apply these days, and just continue living as they had been, which fortunately is what most do.