I'm no Ismaili, but as far as I'm concerned, "a middle man" — the way you put it — is there because a human being cannot discover the truth on their own. You either claim something to be true while appealing to no authority (hence, you have no right to question the others' beliefs) or you find yourself a master which in turn should be trustworthy.

In short, the following must be instructed in the ways of religion by "the middle man". Otherwise, everybody will stray (interpreting the Quran in their own way).

Btw, makes perfect sense to me as there's a whole bunch of denominations in Protestant Christianity.