Comment 17 for bug 326135

This is very unpleasant feature that shouldn't be present in ubuntu.
It isn't security hole only.

For example adding user to 'audio' group breaks fast user switch, because the users audio continues to play
even when other user is active.

Since these unix groups seems to be abandoned, the right solution I think is to remove that settings page.
Users that have advanced needs (don't run desktop for example), can still happily use these settings

Maybe even better just allow user to edit the groups the user is in, but without misleading descriptions that are in place.