This can be illustrated by the ancient Hindu tale of the blind men and the elephant in a room. In order to determine what is in the room with them, the blind men resort to their sense of touch. The blind man who feels a leg says the elephant is a tree trunk; the one who feels the tail says it is a rope; the one who feels the trunk says it is a tree branch; the one who feels the ear says it is a fan; the one who feels the belly says it is a wall; and the one who feels the tusk says the elephant is a solid pipe.
The pluralistic assumption is that all of the men are correct. They based their view of the elephant on what they had experienced. This tale is set before Christians as a lesson that all religions are correct in their approach to God, but none of them can fully grasp Him.
There are two main flaws in this argument. First, the assumption is that all of the men are correct is false. The fact of the matter is that all of the blind men were wrong. Thus applied to religion, pluralism is tantamount to atheism, since the only way all religions can be equal and valid is if they are all wrong. Second, it is based in a denial that God has revealed Himself. This is precisely what Christianity holds. The "elephant" has proclaimed what he is, and gave the blind men eyes to see him.
"Blessed are you, Simon Bar-Jonah! For flesh and blood has not revealed this to you, but my Father who is in heaven." (Matthew 16:17)