Many Catholics suffer from what I would call a truth complex. They are embarrassed to say that the fullness of the Truth is in Jesus Christ. Some symptoms of this complex are an evasion of any opportunity to speak about the faith, a reluctance to defend Catholic doctrine when it is mocked or ridiculed, and a conviction that the Catholic faith must be lived privately. And the main causes of the truth complex in Catholics are: either a lack of faith triggered by relativist concepts, or a conviction that tolerance and "coexistence" are supreme values.
The first symptom: relativist concepts. If truth is relative, isn't the Church exaggerated in her claim to fullness of the Truth? We should probably start with the basics, like always, to answer the question. Most people agree that there is a right answer as far as material reality goes. Water contains hydrogen and oxygen. Two plus two equals four. The chair that you are sitting on exists, if not you would fall.
The same can be said of spiritual reality… not of your personal experience of spirituality, but of spiritual reality in itself. You may experience that God exists, or you may not, or you may sometimes experience His presence, and other times experience His absence. Regardless of your personal experience, however, either God exists, or He does not. The same goes for other spiritual realities: when you die, either your entire being will be extinguished and your body will remain in the grave, or it will not. Your life either has intrinsic meaning, or it does not. After death, it cannot be equally true that something will happen and that nothing will happen. It cannot be equally true that you will be reincarnated or that you will go to Heaven or Hell.
There are many truths that are subjective and changing, but not all of them. The way we experience spiritual reality can be different— even within the Catholic Church there are thousands of movements and spiritualities that experience Catholicism in different ways— but again, there are certain basic truths that do not change, regardless of how we feel about them.
The other symptom of the truth complex is the conviction that tolerance and "coexistence" are supreme values. One of the classic “proofs” that the Catholic faith is credible is the sublime nature of her doctrine. The exceeding beauty, the sublimity of the Catholic Answer is rooted in her concept of love. God Himself was made flesh to teach us how to love— love until death, until the Cross. We are called to have this same love for one another and it is much more than “tolerating” or “coexisting.” If your faith is sincerely rooted in Catholic doctrine, the stronger your faith is, the more universal your love should be: love without prejudice, without discrimination, regardless of the beliefs that others choose to profess. That profound faith will lead you to see the “seeds” of truth and the beauty that can be found in different religions.
It doesn’t make sense for Catholics to have a truth complex, to be embarrassed to recognize that the fullness of the Truth can be found in Jesus Christ, in the Church He Himself founded. In the Encyclical Lumen Fidei, the Holy Father points out that if I live according to the Catholic faith, I don’t exactly possess the Truth, the Truth possesses me; the truth envelopes me, and that should lead me to humility, not pride. There can never be anything offensive (to others) or embarrassing (to you) about believing in the truth of the Catholic faith— and sharing it! —if you understand what it means to be Catholic.