I want to completely remove Unity-2D (not Unity) on Ubuntu Precise Pangolin 12.04. I used dpkg -l | grep unity-2d to list the packages which belongs to Unity-2D. The result was this:

 ii  libunity-2d-private0    5.12.0-0ubuntu1.1    Unity 2D shared library

 ii  unity-2d                5.12.0-0ubuntu1.1    Unity interface for non-accelerated graphics cards

 ii  unity-2d-common         5.12.0-0ubuntu1.1    Unity 2D Panel

 ii  unity-2d-shell          5.12.0-0ubuntu1.1    Dash and Launcher for the Unity 2D environment

 ii  unity-2d-spread         5.12.0-0ubuntu1.1    Unity 2D Spread

Now I want to remove those packages with:

 sudo apt-get purge unity-2d unity-2d-common unity-2d-panel unity-2d-shell unity-2d-spread libunity-2d-private0

Then I get a the following message:

The following packages will be REMOVED:

  libunity-2d-private0* ubuntu-desktop* unity-2d* unity-2d-common* unity-2d-panel* unity-2d-shell* unity-2d-spread*

which means that the package ubuntu-desktop should also removed. But the decription from that package apt-cache show ubuntu-desktop says:

Description-en: The Ubuntu desktop system

 This package depends on all of the packages in the Ubuntu desktop system

 .

 It is also used to help ensure proper upgrades, so it is recommended that

 it not be removed.

that it should not be removed, because it is needed to ensure a successful system-update.

How can I remove Unity-2D without removing Ubuntu-Desktop?