As much as we may not like WD’s reply, they are right. The device for all its flaws (and poor programming) is what it is, people’s expectations (sometime unreasonable) are what they are. The device doesn’t officially have the capability to disable or turn off the Public Share. If that is a problem then either; go the unofficial route mentioned above, live with it and don’t put anything in the Public Share directory, or as WD suggests find another NAS device that meets your expectations.
The sad fact is there are several issues that WD should address but; has not, will not, and probably never will address. These includes, beyond the Public Share issue, the remote mapping feature and Windows Phone app that were both removed when WD went to OS 3 firmware. There is now a workaround for the remote mapping issue (see link below) but so far no good workaround to the lack of a WD app for Windows Phone users.