Stalin is a great example of what happens when faith obscures rationalism. Stalin was an atheist but primarily he was filled with faith in (his nasty version of) marxism such that even when it was demonstrably shown to be harmful to the people it was persisted with and preached. A true rational thinker , in a position of leadership and power, will be willing to alter their underlying assumptions and premises based upon evidence and feedback.
Intellectual honesty and rationalism is to perpetually doubt everything. Faith is to perpetually assume that the object of your faith is right no matter what. Faith can never equal intellectual honesty as it is unwilling to examine itself in a questioning or doubting state. Faith can never doubt itself lest it cease to be. Worldviews built on faith are difficult to dislodge no matter how wrong they are hence we have a plethora of competing religious ideas which are mutually incompatile but rely on exactly the same subjective evidences.
Faith is the problem imo. Atheism is not a recipe for removing faith ( as Stalin showed) but it is a darn good start for getting rid of one idol that relies on faith.