The Church teaches, by the reign of Leo XIII, that all naturalism is erroneous and insidious.
It is the teaching of the Church that we cannot take reason only as our guide.
Leo XIII, in Humanum genus, condemns naturalism: “The fundamental doctrine of the naturalists, which they sufficiently make known by their very name, is that human nature and human reason ought in all things to be mistress and guide. Laying this down, they care little for duties to God, or pervert them by erroneous and vague opinions. For they deny that anything has been taught by God; they allow no dogma of religion or truth which cannot be understood by the human intelligence, nor any teacher who ought to be believed by reason of his authority. ”
The Church also condemns Masons for welcoming men from any religion into their group. Why? Why should such a practice be so worrisome? Pope Leo links it to indifferentism:
“Again, as all who offer themselves are received whatever may be their form of religion, they thereby teach the great error of this age-that a regard for religion should be held as an indifferent matter, and that all religions are alike. This manner of reasoning is calculated to bring about the ruin of all forms of religion, and especially of the Catholic religion, which, as it is the only one that is true, cannot, without great injustice, be regarded as merely equal to other religions.”
How tempting it would be to form a group in which Catholics and non-Catholics, Christians and non-Christians, can work together. Yet, as Leo teaches, how greatly it risks indifferentism.
Leo also condemns the notion that authority is given to the commander by the subjects. That is, he condemns the idea that one must receive authority from those whom one is to govern. Let us hear what is the false naturalism that he condemns:
“22. Then come their doctrines of politics, in which the naturalists lay down that all men have the same right, and are in every respect of equal and like condition; that each one is naturally free; that no one has the right to command another; that it is an act of violence to require men to obey any authority other than that which is obtained from themselves. According to this, therefore, all things belong to the free people; power is held by the command or permission of the people, so that, when the popular will changes, rulers may lawfully be deposed and the source of all rights and civil duties is either in the multitude or in the governing authority when this is constituted according to the latest doctrines.”
Connected to this error is the error that society is best constructed without religion. Or, that the religion should not be specific. These he condemns as errors:
“It is held also that the State should be without God; that in the various forms of religion there is no reason why one should have precedence of another; and that they are all to occupy the same place.”
Because of Original Sin, Leo adds, human nature is greatly weakened. So much so that we absolutely need the helps of supernatural grace and the One True Religion in order even to live decently: “20. Moreover, human nature was stained by original sin, and is therefore more disposed to vice than to virtue. For a virtuous life it is absolutely necessary to restrain the disorderly movements of the soul, and to make the passions obedient to reason. In this conflict human things must very often be despised, and the greatest labors and hardships must be undergone, in order that reason may always hold its sway. ”
Hence, we cannot form groups that stress the capacities of human nature, that by intention wish to avail themselves simply of the helps of nature, that make unwelcome any mention of the Catholic faith and the Prince of Peace, Jesus Christ, that welcome any member regardless of his religion in such way as to downplay the absolute centrality of the correct religion in all of life, etc.