There is no need to copy objects for multiple threads to refer to them. It's just that there is a single owner, and the other threads have a non-owning view on

There is no need to copy objects for multiple threads to refer to them. It's just that there is a single owner, and the other threads have a non-owning view only. You need strict control on the thread lifetime, which is enforced through the same single ownership system, in order to enforce this.