Class::InsideOut does require the developer to consider whether one's attributes are public, private, or read-only

Well, perhaps it's clearer to say that Class::InsideOut emphasizes the decision through a choice of syntax.

Class::InsideOut tries to require as few things as possible:

1. Objects: All new objects must be passed to (or created by) the register() function
2. Properties: All data structures for object properties must be passed to the property() function.
3. Direct Access: The key to directly access the property for an object in a property hash must be generated using refaddr() (from Scalar::Util) or the shorter alias id().

The public(), private() and readonly() functions just call property() with appropriate options.

I agree that showing it in practice rather than explaining all this is more appropriate for a primer