"can also explicitly prohibit anyone from using it without violating GNU GPL"
A point of order: Publishing a program under the GPLv3 and including that would probably be a "further restriction" within the meaning of section 10 of GPLv3.
This seems similar to what happens when programs are released under the GPLv3 but say they're only for "non-commercial use" or "personal use only" or some such thing.
The GPL's answer to these types of situations is: "If the Program as you received it, or any part of it, contains a notice stating that it is governed by this License along with a term that is a further restriction, you may remove that term..." :)
