Though the children of this world be wiser than the children of light, their snares and their violence would undoubtedly have less success if a great number of those who call themselves Catholics did not extend a friendly hand to them.
Yes, unfortunately, there are those who seem to want to walk in agreement with our enemies and try to build an alliance between light and darkness, an accord between justice and iniquity, by means of those so-called liberal Catholic doctrines, which, based on the most pernicious principles, adulate the civil power when it invades things spiritual and urge souls to respect or at least tolerate the most iniquitous laws, as if it had not been written absolutely that no one can serve two masters.
They are certainly much more dangerous and more baneful than our declared enemies, not only because they second their efforts, perhaps without realizing it, but also because, by maintaining themselves at the very edge of condemned opinions, they take on an appearance of integrity and irreprehensible doctrine, beguiling the imprudent friends of conciliations and deceiving honest persons, who would revolt against declared error. In this way, they divide the minds, rend the unity, and weaken the forces that should be assembled against the enemy.
By Pope Pius IX
Letter to the president and members of the Saint Ambrose Circle of Milan
March 6, 1873, in I Papi e la Giovent
(Rome: Editrice A.V.E., 1944)