I touched on this in a cousin comment, but freedom 0 of the GPL states categorically that the user has:

>The freedom to run the program as you wish, for any purpose

Redistributing modified versions of the software it what is regulated under the GPL and other copyleft licences. Even then, the main aim of this restriction is to subvert the system of copyright which works in the opposite way (and unlike copyleft, is not just an academic concern, being constantly wielded by people and companies as a weapon against free speech).