Integrity can be defined as loyalty to a principle. It can therefore be understood in terms of Moral Foundations Theory. Intellectual integrity can be defined as loyalty to the principles of Reason and evidence. Liberals tend to score lower on the Loyalty/Betrayal measure than conservatives. We do see evidence of lower intellectual integrity among liberals - they are often flagrant violators of Reason and Logic (see previous post on Laurie Penny). In The Uses of Pessimism, Roger Scruton in coined the phrase 'unscrupulous optimism' to describe the Utopian thinking of the Left. They are often guilty of making the most optimistic assumptions and deriving the most optimistic extrapolations from them. They want their dreams to come true and they'll stop at nothing to see that they do. Liberals frequently employ the most unscrupulous tactics to argue their case because they do not care much about intellectual integrity - they are intellectually unscrupulous. The loyalty that they feel is towards 'the vision'; you cannot sustain loyalty to Reason if you are committed to an imagined Utopia. In fact, very soon the ends come to justify the means.