As you point out, this isn't really the issue - the issue is accidental interference rather than deliberate trespass.

Deliberate trespass in your own codebase isn't something you fix in software, it's something you fix by going over to someone's cube and removing their mouse balls until they get the point. Anyhow, if you can't trust your fellow coders to not play symbol table / reflection / etc type games, you have problems! So folks think they have encapsulation, but they don't, and they think they have loose coupling, but they don't.

Encapsulation is mainly in existance to enforce clean boundaries between objects, and ideally these boundaries should be limited to a very small list of methods and few variables, such that changes in the objects don't break programs.

Furthermore, encapsulation can be broken with no access to variables, by virtue of having trivial getter/setter methods encapsulation IS broken, because the parameters of your object can be tweaked without asking the object nicely. Most folks already know this, but at least in the java world, many don't!