> As I've already told you, using cannot be used in certain situations where reference counting can.
That's like saying that C++ destructors cannot be used in certain situations where refcounting can: it doesn't make any sense. Refcounting works just as well in C# as it does in C++, you just have to implement the refcounting logic in your Dispose method, similar to how shared_ptr implements its refcounting logic in the destructor. And actually, alankila already pointed this out, so I don't even know why I bother repeating it...
> You wouldn't, because you'd use a ref-counting pointer such as std::shared_ptr.
You would, because if you end up holding a reference to an object with refcount 0, that means you forgot to increase the reference count at some point, and that is perfectly possible with a shared_ptr<T>. You could call .get() on the shared_ptr<T> and store the returned T* somewhere. Or, more subtly, you can write a function that takes a T& and then stores that reference somewhere else. Then you pass *t (where t is a shared_ptr<T>) to that method and you've blown it.