Bits and pieces of response - 'a convincing case that almost all bad choices and behaviour in Forest stem from fear' -this is a fascinating point and I've been running my mind over each book thinking of examples and there are many. The worst fear seems to be fear itself; Peter in particular makes idiotic choices because he is afraid of being thought to be afraid.
The obvious exception might be Lois; what she does to Nicola in EOT and CT is purely malicious, she has nothing to be afraid of - but then perhaps her dislike of Nicola stems back to her originally being afraid of Rowan's bad opinion, or, after the disastrous hike, being afraid of being seen to have failed. A fear of losing face perhaps.
EOT is definitely Patrick's best book, isn't it. All that poetry reciting on the ride home though - only a boy in a book could do that.
Tim, on the other hand, always seemed very true to life - I remember bitchy, fickle girls who made me feel, as Nicola does, that it was odd to have a friend who seemed to dislike you so much, if she was a friend, and if it was dislike. I think some of Tim's nastiness comes from her frustration at being trapped in a place where she doesn't belong and doesn't value any of the supposed ideals of the community. Seeing Esther upset at having to be trapped there all half-term when everyone else can escape, probably brought out her sympathetic side.