Boone: there needs to be some compromise between general safety and the known threat level.
To use a real world example, taken from Australian Army doctrine:
The lead scout in an infantry section will have his weapon on "instant" (safety catch to fire), and possibly his finger on the trigger. The number two scout will also be on instant, but more likely to have his finger outside of the trigger guard.
Other members of the patrol will be at "action" - weapon ready, but safety catch to safe.
In a secure zone, or inside an AFV, weapons may be required to be kept at the loaded condition (mag on but no rounds in the chamber).
Certainly, PCs with a good reason to expect an attack should be as ready as possible for an attack. But where an attack is reasonably unlikely (frex, travelling through a patrolled, civilised area), why risk accidental discharge?
I don't see a problem with DMs allowing weapons to always be ready and armour always on, but neither do I see that as being an accurate representation of how adventurers would operate. Of course, YMMV.
Carnifex:
