An intelligent and informed response to the world requires a complex psychophysical organism. However, the inner workings of such an organism impede intelligence and encourage disinformation!
What is a reasonable policy for a small community that has come through a world catastrophe?
trade with other communities;
improve general living conditions;
seek new knowledge of the world, particularly of how it has changed since the catastrophe.
What do some groups in works of fiction do?
impose a rigid ideology;
gather military intelligence only for further conquests.
Either such a regime wreaks great harm for a long time or it is overthrown at great cost. It is "the old and protean enemy." See here. Anderson shows reason overcoming instinct and thus defeating the old enemy in Brain Wave.