I had the setting disabled in my gnome-control-center, but because gnome-settings is not running, it's not taking effect.
So in a way, as soon as you run gdm3, you are *forced* to run gnome (or more precisely gnome-settings) to make sure you can disable that setting, otherwise it stays turned on and there is no way to disable that behavior.
To clarify my last comment here:
I had the setting disabled in my gnome-control- center, but because gnome-settings is not running, it's not taking effect.
So in a way, as soon as you run gdm3, you are *forced* to run gnome (or more precisely gnome-settings) to make sure you can disable that setting, otherwise it stays turned on and there is no way to disable that behavior.