Well, I'm not Christian at this point in my life but I've
  noticed through the years that many current atheists were raised
  in homes that were as intense about the version of Christianity
  as they are now in their anti-theism.

  In short, the direction changed, but the intensity remained.

  I never had that intensity.

  In theory, some basic Trinity knowledge should at least be
  present through upbringing. That's an assumption on my part of
  course and even if not, _some_ understanding of it is easy
  enough to obtain simply LIVING in a Western society, just as
  it's easy to obtain a basic level of understanding about Zen
  Buddhism in the form expressed in the West.

  Cultural knowledge.

  But you are correct; it _is_ a hard thing to understand, just as
  QM is a hard thing to understand. In both cases, somebody else
  did the heavy-thinking and we just have to accept it and accept
  trusted authorities, unless we manage to understand it, in which
  case we don't need the authorities for support as much anymore
  because we 'got it'.

  Someone else made the math formulas. We just accept them. etc.
  Now, I don't read the math, but I understand the process of QM.
  Explaining it? Well, it'd take a lot of drawing and I can't draw
  well and words are equally hard to describe it with. It's easy
  when it 'clicks', but explaining it quickly? Not so easy.