Nightmare Fuel: Ivan's and Lise's discussions of child abuse. Lise's introduction of stewed pineapple into the picture does not help.
Strawman Has a Point: The Contra view was not the one Dostoyevsky wanted to endorse. Whether Ivan's expression of his nihilistic views is sufficiently refuted by Alyosha and Zosima is for the reader to decide, but in terms of dramatic impact, the Pro views have hardly the same power as Ivan's accusation. (Which may be why both atheists and devout Christians have said that "The Grand Inquisitor" is their favourite scene in all literature.)
This is common throughout Dostoevsky's works — each character has total consciousness and a coherent worldview, both distinct from the author's and separate from authorial intent.note For those who wish to know more and/or pursue a career in literary scholarship, see the works of Mikhail Bakhtin. Ivan's views do not exactly mirror Dostoevsky'snote It's complicated. but his views are presented as a fully realised argument. Alyosha and Zosima are given equal independence from the author. Ivan is an aversion of this trope (or a Double Subversion, if you look at authorial intent).
Wild Mass Guessing: There is a narrator to the story. The narrator narrates a long scene in which Ivan talks to a devil that no one else can see and that even Ivan thinks is in his own head. Who could possibly know what the devil said in that scene? Well, Ivan...and the devil...And we know Ivan's not the narrator...