The Rule
Characters Should Express Their Opinions, Not Yours
Storyteller: I plan to tell a tale that has a powerful message.
Producer: If you’ve got a message, send it by Western Union.
In real life, the degree to which we'll listen to other people rant about things is minimal. In fiction, it's generally even less tolerable.
Counter-Example
A human being should be able to change a diaper, plan an invasion, butcher a hog, conn a ship, design a building, write a sonnet, balance accounts, build a wall, set a bone, comfort the dying, take orders, give orders, cooperate, act alone, solve equations, analyze a new problem, pitch manure, program a computer, cook a tasty meal, fight efficiently, die gallantly. Specialization is for insects." -- Robert Heinlein, Time Enough For Love
At some point Robert Heinlein couldn't NOT pull out a soapbox in his stories. In the best instances, it plays into later events. In the worst, it might as well be Wade's lubed-up sex-doll. This counter-example is a much-beloved quote—I even used "Specialization is for insects" ironically in Wingless, which is about hyper-intelligent and fastidious beetles.
But no one ever says, "Wow, that quote really moved the book along."
Commentary
In two distinct places in Ready Player One, Cline stops to tell the reader what he thinks: First about God and next about masturbation. In both places the story comes to a complete halt and neither has any effect on anything else in the book. The POV expressed is so amazingly one-sided that it reveals the author and his main character One Of Me as very shallow thinkers and rather bigoted.
Cline could've introduced some doubt. For example, the only person in his physical environment who's ever been nice to him is religious--but nowhere in his screed does he suggest that her belief in "a guy named 'God'" might have something to do with that. Nowhere in his days-long jerk-off-fest does he consider what impact pornographic immersion and instant gratification might do to his character.
It's not even a question of "agree" or "disagree". But "of course we all believe the same things as me and there are no other valid viewpoints" is a particularly boring one.
But even well done, the story would be better served without these passages.*
*This website is not a counter-example. It's definitionally a rant about writing.