An imam who knew him diagnoses Sayfullo Saipov's problem. (The New York Times, which interviewed the imam, attributes Saipov's difficulties to "disappointments" and "rootlessness"--in other words, America failed him).
But back to the iman. Could it be that the main disease in the Muslim Community isn't a failure to "learn religion properly" but individual Muslims inculcating core religious teachings--including supremacism and the jihad imperative--all too well?
The other main disease, of course, one from which the imam seems to suffer: denial.
Update: Many infidels suffer from the disease of denial too. For instance, this one.