I'm not worried about malicious users. I'm worried about household guests and family members.
If this switch is on, you can't leave your media (mythtv for example) computer alone with a guest even for 5 minutes! How suckitude is that?
Hence, if you ever have guests in your house and you might want to go to the bathroom while they are there (say using a guest account to surf the web), you must disable this feature. Since the vast majority (73.2%) of home users fall into this category, the majority of users should disable this feature. However we know that the majority of users (97.32%) never disable any default feature until they've been reamed.
The really annoying thing is that the fedora devel list is clogged up by pages upon pages upon pages of this thread.