The folder "System" can't be moved into one of its subfolders. ***WTH?***

[Tasmanian Devil]

6. Drag & Drop

Drag and drop of most files works fine. As long as they are simple files and folders. Where simple means no resource fork (data only), no extended attributes, no setuid bits, no worries about unix file or group ownerships, file names are unique (not case-sensitive), names are not too long, names don't contain special characters, no extended attributes, no symbolic links, no hard links, no sparse files ... etc. etc!

The focus has been to be able to copy normal user files. Using drag & drop to copy system files has always been tricky, as many of those files have special modes (e.g. setuid root), or are locked down or even invisible to try and prevent accidental modification by users. E.g. the ~/Library folders have been hidden by default since the first days of OS-X.

I'll agree that it's silly difficult to copy the OS to a different volume, but it's not something the average mac user has much interest in doing.