Child abuse is precedented, doesn't make it okay.

Straw man.

The most likely parents to exercise a right to read their 16-year-old teenager's online messages would be abusive, controlling ones.

The American stance on children is different. Children are the property of their parents, to raise and indoctrinate however one sees fit.

Luckily everyone grows up and when you're 18 you can move to a Democrat state never entering a church ever again.

That's a further, unsubstantiated assumption of malice.

Some involved, worrying parents want to know their kids aren't getting mixed up with bad lifestyle habits or dangerous persons.