Description of problem:
As part of the wayland test day, I run /usr/libexec/gnome-initial-setup under the user liveuser. It allowed me to create a new user. This is really surprising. If it allowed me to adjust my own user data instead, that'd be understandable.
$ getent passwd foobar
Version-Release number of selected component (if applicable):
If you run it manually, you are the one who decides what the tool does.
Try gnome-initial-setup --existing-user
g-i-s has been around for a while, and people know they can run it to enable/disable privacy settings and such. And g-i-s currently says "Tell us more about yourself". At least, it seems that this choice should be reversed: anaconda/first-boot/whatever-special-thing should use some switch (--create-user), and the default thing should be to do nothing surprising.
it is in libexec for a reason. This is not a tool you are supposed to run by yourself.