Description of problem: The current default of SELinux being enabled (with no option to disable) is (in my own personal opinion) unworkable. Fedora lacks automated, graphical tools for users and administrators to manage simple context changes - for example, downloading an ISO image, setting up a virtual machine, or copying system configuration files from /home into /etc. Many of these operations will be broken by the complexity of the SELinux policy in Fedora, while the user will have no easy recourse other than filing a bug and waiting for an update. Rather than forcing users to have SELinux as a means of publicizing the many positive advantages that it offers, it would be more advantageous to Fedora to allow users to make choices for themselves - allowing them to disable SELinux on those systems that do not require it is a prudent and sensible course of action, until such time as the complete user experience is entirely graphical, well understood, and easy for large scale end user usage and deployment.
The System->Administration->SELinux Management option allows all sorts of configuration of SELinux and allows users to disable it from an environment in which they can do some research and figure out exactly what they're doing. Within firstboot there's no web browser or anything similar, so the SELinux combo box doesn't really make a whole lot of sense. Allowing configuration after the user has logged in means they can do some research and figure out what the implications of disabling SELinux are, and can then choose to do so with the tool on their desktop.