Religious pluralism, that is the principle of allowing a peoples with different religious beliefs, without penalty or favoritism from its government, to coexist in a civil society, is a principle that honors each and everyone's will to their own religious beliefs. However, theologically, there is no such thing as religious pluralism.
First, to believe that all religions are equal or that the true complete revelation of Jesus Christ exists in some totality of all Christianity is contrary to the teachings of the Catholic Church. First, the declaration put forth by the Congregation of the Doctrine of Faith Dominus Iesus - On The Unicity and Salvific Universality of Jesus Christ and the Church (DI) declares
Furthermore, “Jesus Christ, therefore, the Word made flesh, sent ‘as a man to men', ‘speaks the words of God' (Jn 3:34), and completes the work of salvation which his Father gave him to do (cf. Jn 5:36; 17:4). To see Jesus is to see his Father (cf. Jn 14:9). For this reason, Jesus perfected revelation by fulfilling it through his whole work of making himself present and manifesting himself: through his words and deeds, his signs and wonders, but especially through his death and glorious resurrection from the dead and finally with the sending of the Spirit of truth, he completed and perfected revelation and confirmed it with divine testimony... The Christian dispensation, therefore, as the new and definitive covenant, will never pass away, and we now await no further new public revelation before the glorious manifestation of our Lord Jesus Christ (cf. 1 Tim 6:14 and Tit 2:13)”. (DI, 5)
This means that the revelation of Jesus Christ is complete and no new revelation is coming or should be expected. Surely, the saints, the doctors of the Church and the Church itself through the Magisterium has and will continue to broaden our intellectual understanding of this complete revelation. But "new revelation" is exactly what other non-Catholic, Christian and non-Christian religions is being proclaimed.
Second, any reduction of the Catholic faith then in of itself tries to supply an "additional revelation" which the Catholic church tells us is not compatible with the Catholic faith. Protestantism is a reduction of the Catholic faith. Dominus Iesus says that Protestantism and many other religions, which may contain universal truths, are considered paths to the one, holy, catholic, and apostolic church - the Catholic church.
Therefore, these separated Churches and communities as such, though we believe they suffer from defects, have by no means been deprived of significance and importance in the mystery of salvation. For the spirit of Christ has not refrained from using them as means of salvation which derive their efficacy from the very fullness of grace and truth entrusted to the Catholic Church. The lack of unity among Christians is certainly a wound for the Church; not in the sense that she is deprived of her unity, but “in that it hinders the complete fulfillment of her universality in history. (DI, 17)
Third, to me it is logical that the Catholic Church is the true path to salvation. For fifteen hundred years only the Catholic Church existed. While the term "catholic" first appeared in the year 107 A.D. when St. Ignatius of Antioch used the term in his Letter to the Smyrnaeans that he wrote to Christians in Smyrna (https://en.wikipedia.org/wiki/Letter_to_the_Smyrnaeans), its use described the set of beliefs in place up until that time, as well as for all perpetuity.
Just as there is one Christ, so there exists a single body of Christ, a single Bride of Christ: “a single Catholic and apostolic Church." Furthermore, the promises of the Lord that he would not abandon his Church (cf. Mt 16:18; 28:20) and that he would guide her by his Spirit (cf. Jn 16:13) mean, according to Catholic faith, that the unicity and the unity of the Church — like everything that belongs to the Church's integrity — will never be lacking. (DI, 16)
To say then that the fullness of truth is a collection of all beliefs would mean that there are many "brides" of Christ -and that would make no sense whatsoever! Also, to admit to the inclusion of non-Catholic Christianity in the full deposit of faith would mean that Christ abandoned his Church.
Fifth, the Catholic Church has something that no other Christian church has - the full legitimate set of Sacraments. The "sacraments are outward signs of inward grace, instituted by Christ for our sanctification." (http://www.newadvent.org/cathen/13295a.htm) I mean, bring on that grace! Who couldn't use more of that supernatural help to get us past our failures and our sufferings?
Sixth, no book can interpret itself. If you have every written anything that someone else has read, you know this to be true. My first experience of this was when I was in college and had to write a short story for an English class. The name of the short story was The Potted Plant and it was a semi-biographical story of my immaturity and my alcoholic mother. The story was the first selected by the professor to be read aloud in class. I listened with astonishment to the many interpretations of my story which were far from my intention.
Only the author of a story can truly interpret it completely and accurately. The Holy Bible can only be properly interpreted by its Author. To claim that the Holy Bible is not so hard that it can be self-interpreted is over-generalizing and reducing the glory of God. The Catholic Church has a single teaching source to guide us through the proper interpretation of the Holy Bible - "the ordinary and universal Magisterium of the Pope and the bishops in communion with him teach the faithful the truth to believe, the charity to practice, the beatitude to hope for." (CCC, 2034)
In closing, "the Catholic faithful are required to profess that there is an historical continuity — rooted in the apostolic succession— between the Church founded by Christ and the Catholic Church. This is the single Church of Christ... which our Saviour, after his resurrection, entrusted to Peter's pastoral care (cf. Jn 21:17) (16)... Therefore, there exists a single Church of Christ, which subsists in the Catholic Church, governed by the Successor of Peter and by the Bishops in communion with him." (DI, 17)