Scientific Method
Truth, being demonstrable, does not require faith.
Includes the explicit and unyielding distinction between proven facts and unproven opinions.
Includes the explicit and unyielding distinction between the method of study and the object of study.
And includes denouncing and fighting the attempts to confuse them with each other.
Perhaps the most important case and example of both is the study of the human being:
What was surreptitiously passed off, both as ascertained and as identity of method and object, is the principle that the scientific method can be applied only to the material scope.
As a result, the corresponding principle was accepted as equally ascertained that in the nonmaterial scope it is not possible to apply the scientific method, thrusting the door open to any kind of arbitrary opinion, accepted without demonstration nor measurement.
Which is a wonderful playground for those aiming at controlling and crushing people, because unaware emotion is a much easier prey than conscious thought.