I disagree: the intent of the GPL is to preserve freedom; the way the GPL preserves freedom is by preventing you from removing it by changing the terms.

If I'm choosing a license for a project, it's important that I know that changes other people make will be available to me under the same terms as my own code.

A license that requires you to make the changes available but allows you to restrict my use of those changes is plainly in contrast with the intent of the GPL.