Wrong again It's probably exactly what you meant; but what you said seems misunderstandable.If my own code is GPL then I have the right to revoke that license and delete it.
Aaaactually, wrong: You can't revoke the GPL. Quoting section 2 of the GPL (version 3): "All rights granted under this License are granted for the term of copyright on the Program, and are irrevocable provided the stated conditions are met."
So you can stop distributing your code under the GPL, and you can start distributing it under a different license as long as it's all your own work. But the GPL remains valid for anyone who received a copy of your software under GPL and never violated its conditions, and those people have the right to redistribute the code under the same terms.
Which is exactly what I said. Do keep up.
D.
The part I did misunderstand is the one where you write "I can't control copies that others may have downloaded". This sounds a bit like "I can't prevent people who have a copy from doing things they're not supposed to", when the real situation is "people who already have a GPL'd copy, and people who receive further copies from those people within the GPL's terms, et cetera perge ad infinitum, continue to have the right to modify and redistribute my code under certain conditions, and there's nothing I can do about that".
And just to try for some clarity from my side: My aim is not primarily to argue with ZXDunny, who just confirmed that we already agree on this, but to be clear towards other (potentially confused) readers about what options are and aren't legally possible in an I-no-longer-love-the-GPL situation.