Christianity is quite simple in the end. I think it has two stages:
1. You are convicted of your sin;
2. You accept the grace of God.
The consequence of these two things is 'love, joy, peace, gentleness, self-control...' etc etc. In particular, judgement of one another is abandoned - it is left up to God.
And obviously these things are more or less embedded in us, and we make mistakes etc etc. But this is the 'road map for holiness'.
Fundamentalism is formed when either of these two stages are ignored or belittled.
When 1. is put aside, then the self-righteous Pharisee is formed, and there are judgements left, right and centre.
When 2. is ignored, you get the fear-driven apocalypticism, like Left Behind, and you get the semi-fascist imposition of order, to prevent sin from happening.