I picked up that word in THE Encyclical knowned as UBI PRIMUM by POPE LEO XII ON HIS ASSUMING THE PONTIFICATE MAY 5, 1824How could our Pope of a happier time, be able to describe VII so well:
The current indifferentism has developed to the point of arguing that everyone is on the right road. This includes not only all those sects which though outside the Catholic Church verbally accept revelation as a foundation, but those groups too which spurn the idea of divine revelation and profess a pure deism or even a pure naturalism. The indifferentism of Rhetorius seemed absurd to St. Augustine, and rightly so, but it did acknowledge certain limits. But a tolerance which extends to Deism and Naturalism, has given every individual a wide freedom to embrace and adopt without danger to his salvation whatever sect or opinion appeals to him on the basis of his private judgment. The apostle Paul warns us against the impiety of these madmen. "I beseech you, brethren, to behold those who create dissensions and scandals beyond the teaching which you have learned. Keep away from such men. They do not serve Christ Our Lord but their own belly, and by sweet speeches and blessings they seduce the hearts of the innocent."
15. But Oh! the depth of the riches of the wisdom and knowledge of God! How incomprehensible His judgments! God, who destroys the wisdom of the wise, has clearly given the enemies of His Church, who despise supernatural revelation, a perverted mind corresponding to the symbol of iniquity which was written on the forehead of the wicked woman in the Apocalypse. For what greater iniquity is there than for those proud men not only to abandon true religion, but also to seek to ensnare the imprudent by criticisms of every sort, in speech and writings filled with all deceit! Let God arise and restrain, make futile and destroy this unbridled license in all its manifestations.
Take the time to read the entire Encyclical avoiding reading my notes and quotes out of context
Sedevantism does not have it wrong.