What does Beatty's speech about Clarisse reveal about him; why does he speak about her so passionately?

Beatty is passionate in that he dismisses Clarisse and her family as "odd" and counter to what is "normal" thinking. Beatty is in fact very intelligent. He understands the other side, the side of knowledge and depth. Beatty just chooses to dismiss it; he is too entrenched in the official ideology.