According to a couple of studies, one of them by a psychotherapist who treated these priests for 20 years, the main causes were insufficient candidate screening and insufficient training to prepare for the challenges of celibacy.
You mix those insufficiencies with the Church’s power and authority and with the morbid shrewdness of those priests targeting vulnerable kids and you get these events.
Trying to think about it in terms of mental models the lesson seems to be: don’t give moral power and authority to too many people (where bad apples are likely to appear) in demanding situations (we are wired for reproduction). Corollary: if you devise such a system and you find issues (in this case children being raped) don’t cover it up and expect the problem to disappear.
What about the journalists?
The Spotlight team are heroes: in my mind they are kind of using the scientific method (make hypotheses, test them, refine them, keep a skeptical mind) to uncover new knowledge about human nature and their findings can have as much impact as many more traditional scientific discoveries like this story or others like Watergate.
Back to the movie: I didn’t find it lurid. The acting was strong and the plot gripping. Recommended.