Maybe the question is framed backwards. Instead of "What is present in
us that caused us to do this?", maybe it should be "What is absent in us?"
Here's what I mean. Religious people appear to have a deep need that is
filled by their religion. I personally know some (OK, 1) JW who is intelligent
and analytical. Yet, even when presented with apostate evidence, still refuses
to see the point.
I personally do not feel a need for the structure that either religion or God
provides. Maybe that's the difference.