An open source license, such as the GPL, does not neccesarily give you the right to use the name, it's true. If the name is trademarked, the trademark holder can try to prevent you from using it, and that has happened.
But if we go back to the _point_ of open source, especially the GPL: It's to let users keep using and modifying and distributing modifications to the software, without needing the permission of the original authors. That's the whole point, for users to have that freedom, that the authors can not take away from you. That sourceforge can keep distributing the software without the permission of the original authors is the entire point.
To the extent that trying to prevent third parties from using the name makes it harder to distribute the software (for instance, would it require changing the source to take the name out? Would it make it harder for users to find software that the authors are _trying_ to suppress?), I think we could argue that it would be against the spirit of the GPL, regardless of what trademark law says.
But if we go back to the _point_ of open source, especially the GPL: It's to let users keep using and modifying and distributing modifications to the software, without needing the permission of the original authors. That's the whole point, for users to have that freedom, that the authors can not take away from you. That sourceforge can keep distributing the software without the permission of the original authors is the entire point.
To the extent that trying to prevent third parties from using the name makes it harder to distribute the software (for instance, would it require changing the source to take the name out? Would it make it harder for users to find software that the authors are _trying_ to suppress?), I think we could argue that it would be against the spirit of the GPL, regardless of what trademark law says.