Rico, I'm pretty sure we're agreeing... Because I'm not at all talking against someone who established the rules beforehand, laid it out for their children. That's fine by me. I'm am A-OK with the strict lay-down-the-law kind of boundaries you're talking about.
Parent's SHOULD be "nosy." They should be in their kid's lives. But they need to be clear about the extent of that.
If it's something like "Once a week when you're not home I'm going to go through your room." or "Every month I'm going to read your text messages." The child should be informed. If you have NOT been doing those things, then you have by omission already established a boundary.
Teenagers, for one, are pretty smart. You can talk to them less like a child, and more like an adult. And informing them of what you're doing, such as changing the rules and boundaries, is a sign of respect. And while some parenting guides will tell you that you aren't supposed to be your child's friend, but their parent, you still need to have a relationship of mutual respect.
"Peppered" as my opinion may be, it's the same one I had before and after the incident. It's why it bugged me so much when they randomly decided to do it.