Pope Leo XIII recognized this in his 1896 encyclical Satis cognitum, in which he discoursed at some length on unity as a mark of the Catholic Church.

Pius XI rejected the hope: that the nations, although they differ among themselves in certain religious matters, will without much difficulty come to agree as brethren in professing certain doctrines, which form as it were a common basis of the spiritual life.

Certainly such attempts can nowise be approved by Catholics, founded as they are on that false opinion which considers all religions to be more or less good and praiseworthy, since they all in different ways manifest and signify that sense which is inborn in us all, and by which we are led to God and to the obedient acknowledgment of His rule.

turn aside to naturalism and atheism, as it is called; from which it clearly follows that one who supports those who hold these theories and attempt to realize them, is altogether abandoning the divinely revealed religion.

[2]Pius understood this idea that all religions are just varying (and fallible) human expressions of a natural religious impulse or instinct.