«فلان فاسق إلا أنه جاهل»
He is morally corrupt, and, as if that were a concession, he is ignorant as well.
The opening judgment establishes the defect of corruption, and the exception-like turn introduces ignorance, a second defect. What seemed capable of softening the blame only increases it.
The first type begins by denying merit; the second begins by establishing a fault. Keeping this distinction clear prevents confusion between the two modes of emphatic blame.