Alan Kay isn't going to agree that you should simply pass structures around and use element-level procedures. Message passing as a concept is a higher order version of what you see in C++, not what you see in C. A big reason Kay dislikes C++ is because it doesn't go far enough in terms of dynamic dispatch and the ability to substitute implementations dynamically at runtime. One way to put it is: C++ makes decisions at compile time that should be made at runtime.

What you are saying certainly applies neatly to getters and setters, but consider that classes are used for far more complex use cases than as a simple data holder. Indeed, if all you need is to store two integer components, you might not need a class.

Of course, in Smalltalk and it's ilk, you only have objects. So there is no opportunity to access data from within a structure (externally) without passing messages.