The vast majority of iPhone users won't consider it a betrayal that they can't send images of child abuse, any more than they consider it a betrayal that it doesn't come jailbroken.
The victims of child abuse depicted in these images may well have considered it a betrayal by Apple that they allowed their privacy to be so flagrantly violated on their devices up until now.
The rule is that your (note the emphasis) device won't ever willingly betray you. There's nothing here that implicates the majority in any way. Simply, your own device should never work against you.
This actually sounds like a great rule to prevent this kind of authoritarian scope creep.
Probably neither would child abusers, since as soon as they send an image of child abuse, they're much more likely to be caught than if it had stayed on their phone.
> a betrayal by Apple that they allowed their privacy to be so flagrantly violated on their devices up until now.
"Their" devices? Once Apple sells an iPhone, it no longer belongs to Apple. Taking "betrayal" to mean "didn't plant backdoors on other people's computers to catch your abusers" is stretching that word far beyond reason.