It has been a long time since I worked on an application so trivial that parts of it weren't broken out into separate libraries. Most often, those libraries end up being maintained by people other than their users, and the users always end up using the library in unexpected ways or contexts so these protective measures always become necessary.

Perhaps more to the point, I don't think there should even be multiple constructors each called in different situations that it takes several pages to describe. This complexity mostly exists because the people who defined C++ don't seem to understand the significance of value vs. reference semantics, as the OP also noted. Move semantics and rvalue references represent a tacit omission that the previous semantics were broken, but they just introduce even more non-intuitive syntax and another few pages to describe what happens in which situations. That's exactly the kind of spurious complexity that makes compiler writers want to go on killing sprees and folks like me want to avoid the whole morass.