Why do the collectivists prohibit knowledge of the world "i"?

The meaning of "I" expresses individuality. This society demands conformity. There is no individual; there is only the collective. Equality and the Golden One do not know the Unspeakable Word "I," and because of this, they feel instinctively that they are missing an essential concept in their understanding of the world. Love, in the world of Anthem, is an expression of the kinship of two selves, but without the fully articulated expression of self, they cannot verbally consummate their love. The issue of vocabulary rears its head earlier as well, when the lovers meet by the hedge and try to explain their mutual attraction -- this time by stating that they do not wish to be siblings. Fittingly, once Equality 7-2521 deciphers the Unspeakable Word in his books, the Golden One's first words to him are "I love you" -- signaling the completion of his quest.