I don't think parents should do it just for their own entertainment, but because they are responsible for the health and well being of their child, who is under their care, I would put it into the same category as looking at their social media or texts. If the relationship is a healthy one, usually a parent should have a pretty good idea of what is going on in their child's life. If looking at those things is the sole way they have a window into their child's life, they probably need to be shouldering responsibility to foster more connection to their child. Having said that, there are times when kids will hide things that they think will restrict their freedom or disappoint their parents, yet they don't have the experience or the foresight to be able to see how serious the situation is or know how to deal with it. Again, this is why relationship is really important and actively teaching kids how to talk about difficult things. Parents sometimes need to be prepared to be disliked if it is a matter of their child's safety, since no one else has the authority or information to make decisions that a parent should. They also need to proactively reassure the kid that there's nothing the child can talk about that would be relationship ending. I don't think it is entirely responsible for parents to just take what their kids say at face value without doing a little private detective work of their own. That doesn't have to mean going through their child's private thoughts all the time, but if there is reason to suspect something is up, much better a breech of privacy than a suicide, unaddressed eating disorder or fallout from a sexual assault or something else that is very serious and potentially life changing. Obviously, independence is a gradual handing off of decision making and responsibility and with it comes a greater degree of privacy. However, I see parents doing that at younger and younger ages, because it absolves them of responsibility, the kid prefers it, and it leaves the parent much freer to pursue their own interests and social life, rather than creating a world that includes their older children in it. There also is a tendency for parents to believe that there is something magic about turning a particular age, in terms of maturity springing into being, or that if the child has the trappings of adulthood (job, car, phone, own social circle) that it means that they no longer are needed in an active role. I think many parents over trust their children, or don't have the emotional energy to deal with it if the child is needy or angry with them, so they distance themselves. High school kids are navigating a lot of very new situations and are preparing for adulthood. Just as children who have just learned to ride a bike need more monitoring than a child on foot, so do older children that are navigating newfound independence and responsibility. The goal though should be not to keep people penned up and wield authority as a power trip, nor to cut them loose prematurely, but to give them the tools to launch into capable and productive adulthood. To do so, they need to be involved and aware of what their child is dealing with, but it should stem from a close relationship with them rather than just covert surveillance.