From Patrick Madrid’s coverage on Relevant Radio:

…In light of the scale of the pedophilic misconduct, a word of Jesus has again come to attention which says … “whoever causes one of these little ones who believe in me to sin, it would be better for him if a great millstone were hung around his neck and he were thrown into the sea.” That’s from Mark 9:42. And Benedict says the phrase “the little ones” – in the language of Jesus – means the common believers who can be confounded in their faith by the intellectual arrogance of those who think they are clever…
Like, I don’t know, maybe… certain gadfly priests who flit around on social media and flit around giving talks and lectures and appear on, you know, late night television programs and confound the faith of believers because of their own intellectual arrogance and they subvert the teachings of the church… I don’t know; I’m just pulling ideas out of the air here. He’s referring to that kind of thing.
So here Jesus protects the deposit of the faith with an emphatic threat of punishment to those who do it harm. What he’s saying here, I should just say, is: bishops and priests, take note. Those who cause these little ones who believe in me to sin …. It would be better for him if a great millstone were hung around his neck and he were thrown into the sea. He identifies the little ones from the Greek that’s used there as the common believer – the average person who doesn’t have a theological background. The modern use of the sentence is not in itself wrong but must not obscure the original meaning…