From The Hunger Games:
My bow is a rarity, crafted by my father along with a few others that I keep well hidden in the woods, carefully wrapped in waterproof covers. My father could have made good money selling them, but if the officials found out he would have been publicly executed for inciting a rebellion. Most of the Peacekeepers turn a blind eye to the few of us who hunt because they’re as hungry for fresh meat as anybody is. In fact, they’re among our best customers. But the idea that someone might be arming the Seam would never have been allowed.
I'm not sure I understand why the sentence uses would never have been instead of would never be. The protagonist's father died a long time ago; that's why she's talking about him in the past tense. The book itself is written in the present tense. The Seam is the district where the protagonist lives.
Here's my guess:
If I rewrote the sentence in the present tense, I think I'd get:
But the idea that someone might/may be arming the Seam has never been allowed.
To make it hypothetical, I would need to replace has with would have; I also wouldn't be able to use may:
But the idea that someone might be arming the Seam would never have been allowed.
I suppose would never be would work if the present tense version used is never:
But the idea that someone might/may be arming the Seam is never allowed.
But the idea that someone might be arming the Seam would never be allowed.
The difference is that this version refers only to the present while the original sentence refers to the past up to the present.