What is wrong with C++'s OOP?

It's not that there's a problem with C++'s OOP. It's that OOP itself is the problem.

Alexander Stepanov, author of the STL component of the Standard C++ Library has this to say:

Yes. STL is not object oriented. I think that object orientedness is almost as much of a hoax as Artificial Intelligence. I have yet to see an interesting piece of code that comes from these OO people. In a sense, I am unfair to AI: I learned a lot of stuff from the MIT AI Lab crowd, they have done some really fundamental work: Bill Gosper's Hakmem is one of the best things for a programmer to read. AI might not have had a serious foundation, but it produced Gosper and Stallman (Emacs), Moses (Macsyma) and Sussman (Scheme, together with Guy Steele). I find OOP technically unsound. It attempts to decompose the world in terms of interfaces that vary on a single type. To deal with the real problems you need multisorted algebras - families of interfaces that span multiple types. I find OOP philosophically unsound. It claims that everything is an object. Even if it is true it is not very interesting - saying that everything is an object is saying nothing at all. I find OOP methodologically wrong. It starts with classes. It is as if mathematicians would start with axioms. You do not start with axioms - you start with proofs. Only when you have found a bunch of related proofs, can you come up with axioms. You end with axioms. The same thing is true in programming: you have to start with interesting algorithms. Only when you understand them well, can you come up with an interface that will let them work.

There are two ideal kinds of OOP that are quite different from one another: multimethods, and message-passing. They are best exemplified by Common Lisp and Smalltalk, respectively. In ways, C++ is more like multimethods and Objective C is more like message passing.

Except that objective C does a decent job emulating Smalltalk, and C++ does an absolutely horrid and terrible job emulating CLOS.

Java and C# were then inspired by C++, not the venerable progenitors of OOP, and so now OOP has completely lost face because nobody even remembers what the hell it is.