default visibility of C++ class/struct members

Question

In C++, why is private the default visibility for members of classes, but public for structs?

Answer 1

Because a class is a usual way of doing object orientation, which means that member variables should be private and have public accessors - this is good for creating low coupling. Structs, on the other hand, have to be compatible with C structs, which are always public (there is no notion of public and private in C), and don't use accessors/mutators.