A militia is definitely not something that you would want to have during standard operation and should be forbidden (it already is due to neglect of duty, trespassing, possession of contraband, assault, ...).
During non-standard operation (i.e. shits fucked) there is enough wiggle-room to ignore certain existing regulations if it ensures the survival of the station.
A official IC policy that determines if, when and how a "militia" can be formed would acknowledge that the station regularly faces threats that can wipe out the entire security department.
Otherwise there would be no need for a official ic policy that regulates that.
Therefore I am heavily opposed to the idea of a IC policy.