Kids Don’t Have a Right to Privacy
We wish parents would understand that telling their kids they don’t deserve basic human decency because they live under their roofs does more harm than good. Children are more likely to live recklessly, not visit, and not care about their parents’ welfare when they finally move out of the house.
Source: Reddit
You said they can only be “free” when they move out. So, you can’t blame them for abusing their freedom when you starved them of it for 20+ years. Moreover, this “freedom” isn’t something insane; it’s their privacy. This parent clearly doesn’t think so. To them, their kids are property.