During medieval times, the church was of course the overwhelming influence, and to be a philosopher was to be a theologian. Theology only really started to be questioned during the Renaissance. But that wasn’t to say that there was a unity of thought before that – there was always controversy, debate and heretics.
St Augustine of Hippo (around 400, not to be confused with the one who came over to English shores to preach around 600) set up a monastic community in Hippo, Algeria. He wrote two important works – “The Confessions”, which included lots of interesting stuff about life in the Roman Empire as well his wayward youth, and “The City of God”.
In the 5th century, there was an important theological and philosophical dispute between St Augustine’s concept of original sin and that of Pelagius.
The Augustinian view of human nature held that original sin existed and that there was a predisposition to evil for which God was needed to lead us to salvation.
Pelagius’s “heresy” on the other hand asserted that humans were naturally inclined to good, without necessarily needing the intervention of God.
It is true that evil can for the most part be put down to ignorance, small mindedness and egoism. Hannah Arendt famously spoke of “the banality of evil” after the trial of Eichmann. But the adage “to know everything is to forgive everything” only goes so far. We know that pure evil can exist in individuals. It is documented from the beginning of human history, firstly in myth and then in the first reliable historical accounts (Suetonius’s account of Caligula).
The Augustian view of human nature is the correct one.