As any parent of adolescents has probably experienced, life has become sufficiently complex that emotional maturity by the end of teen years is a thing of the distant past. If adolescence would only be over by 25!
More seriously, for democracy to function representatives need to make critical value trade-offs for citizens. But how can citizens send messages on how they would like their values to drive policies when the issues are so complex that very few citizens — and not too many politicians either — really understand enough of what might happen and at what probabilities to know how to make decisions that do optimize the value signals from citizens.
The ultimate in irrationality is to make a decision that doesn't even advance your values because the situation is so complex that the decision makers — or the public — can't see clear connections between specific policies and their potential outcomes (as one who works on the global warming problem I see this conundrum all the time).
The capacity to be literate about scientific and political establishments and their disparate methods of approaching problems is a good start, but such literacy is not widespread and the complexity of most issues sees public and decision-makers alike disconnected from core questions. Educational establishments often call for more content in curriculum to redress this issue, but I think more understanding of context of scientific debate and political and media epistemologies will go further to build the needed literacy.