Could you please post a more intelligible explanation for beginners. This no autologin issue makes it a pain to use the OS at home. I had uninstalled Windows 7 from it, thinking Linux Mint was somewhat user friendly...not your fault, my mistake. But I guess at least my laptop's "login screen looks really nice" now, as someone you may know said.
I'm working on this right now.
- MDM's PAM policy (in /etc/pam.d/mdm) was fixed a while ago to include "auth sufficient pam_succeed_if.so user ingroup nopasswdlogin"
- As of version 1.4.8, MDM's postinst was still missing the creation of the nopasswdlogin group though. So in Mint 16 for instance, by default there is no group called "nopasswdlogin". You can verify this with "getent group nopasswdlogin". If it returns nothing, you can create the group with "sudo addgroup --system nopasswdlogin".
- I'm not sure about KDE, MATE and Xfce.. I need to test more, but in Cinnamon 2.0, the "Users and Groups" tool doesn't automatically add newly created users to the "nopasswdlogin" group, so you need to click on the groups for the user and add that group yourself. Not setting a password isn't enough.
I'd expect all of this to work out of the box in time for Mint 17, but I thought I'd post my findings here in case people are looking for workarounds.