>Being reported may be seen as betrayal by the parent,

It kind of is no matter how you slice it. You're prioritizing other interests above theirs specifically to their detriment and then saying "it's justified because X". No value for X no matter how legitimate is gonna change the fundametal reality.

>even if it is objectively justified. That could also be the reason why „everyone around“ failed to act,

If everyone around thinks it's justified then they'll have no problem supporting the guy who does want to act. Buuuut, and this is a big bug. "Will support someone narcing on someone to cause the state to take action" is a way higher bar "will support a DIY solution". Showing up to or organizing your friend's intervention is a way lower bar than throwing them under the bus to the cops. What we're discussing here is basically the "lite" version of the latter.