Surveying the modern intellectual scene, the world of public discourse among the educational elites, I conclude that dishonesty does not only reduce the efficiency and effectiveness of thinking - but it actually reduces applied intelligence - probably by re-wiring the brain.
What I am suggesting is that, although the fundamental efficiency of neural processing is an hereditary characteristic which is robust to environmental differences and changes (short of something like destructive brain pathology - encephalitis, neurotoxin, head injury, dementia etc) - habitual dishonesty (such as is mainstream among the modern intellectual elite) will generate brain changes, and a long-lasting (although probably, eventually, reversible) pathology in applied intelligence - such that what ought to be simple and obvious inferential reasoning becomes impossible.
I mean impossible.
Habitual dishonesty (most notable political correctness) is a form of learning; and learning strengthens some brain pathways and brain connections; while allowing other pathways and connections to wither and (perhaps eventually) perish.
Therefore, even on those rare occasions when a typical modern intellectual tries to be honest and to think straight - they cannot do it, because their reasoning processes have been sabotaged by their own repeated habits of dishonesty - their attempts at honest thoughts will be inhibited, and instead channelled down the usual lying pathways...
Thus, in modern intellectual life, honesty is punished and dishonesty is rewarded; honest brain pathways decay, dishonest brain pathways enlarge.
After years and years of conditioning in dishonesty, the typical modern intellectual (whether journalist, scientist, lawyer, teacher, doctor or whatever) becomes physically unable to think straight.
Thus the lack of common sense of the 'Clever Sillies' who rule modern societies, and who are driving them into suicide and self-destruction; may, in practice, be intractable - short of mass repentance and long-term rehabilitation and retraining of neural pathways and connections.
Reference: Clever Sillies - http://medicalhypotheses.blogspot.co.uk/2009/11/clever-sillies-why-high-iq-lack-common.html