For those having trouble with this subject:
Catechism of Pope St. Pius X - First Commandment
15 Q: What else does the First Commandment forbid?
A: The First Commandment also forbids all dealings with the devil, and all association with anti-Christian sects.
Catholic Encyclopedia - Religious Indifferentism
All religions, indeed, may be said to contain some measure of truth; and God may accept the imperfect worship of ignorant sincerity. But it is injurious to God, Who is truth itself, to assert that truth and falsehood are indifferent in His sight. Since various religions are in disagreement, it follows that, wherever they conflict, if one possesses the truth the others are in error. The constituent elements of a religion are beliefs to be held by the intellect, precepts to be observed, and a form of worship to be practiced. Now – to confine ourselves to the great religions of the world – Judaism, Mohammedanism, Christianity, and the religions of India and the Orient are in direct antagonism by their respective creeds, moral codes, and cults. To say that all these irreconcilable beliefs and cults are equally pleasing to God is to say that the Divine Being has no predilection for truth over error; that the true and the false are alike congenial to His nature. Again, to hold that truth and falsehood equally satisfy and perfect the human intellect is to deny that reason has a native bent towards, and affinity for, truth. If we deny this we deny that any trust is to be placed in our reason. Turn to the ethical side of the question. Here again there is conflict over almost all the great moral issues. Let an illustration or two suffice. Mohammedanism approves polygamy, Christianity uncompromisingly condemns it as immoral. If these two teachers are equally trustworthy guides of life, then there is no such thing as fixed moral values at all. If the obscene orgies of phallic worship are as pure in the sight of God as the austere worship that was conducted in the temple of Jerusalem, then we must hold the Deity to be destitute of all moral attributes, in which case there would be no grounds for religion at all. The fact is that this type of Indifferentism, though verbally acknowledging the excellence and utility of religion, nevertheless, when pressed by logic, recoils into absolute Indifferentism. “All religions are equally good” comes to mean, at bottom, that religion is good for nothing.
Pope Pius XI, Mortalium Animos
Certainly such movements as these cannot gain the approval of Catholics. They are founded upon the false opinions of those who say that, since all religions equally unfold and signify- though not in the same way - the native, inborn feeling in us all through which we are borne toward God and humbly recognize His rule, therefore, all religions are more or less good and praiseworthy. The followers of this theory are not only deceived and mistaken, but since they repudiate the true religion by attacking it in its very essence, they move step by step toward naturalism and atheism. Hence it clearly follows that anyone who gives assent to such theories and undertakings utterly abandons divinely revealed religion. "
