Interesting you mention keeping the hammer down given that such carry is considered unsafe. Even the military in 1940 thought the hammer should be down only when the pistol had an empty chamber.
The USN ran extensive tests on the safety of carrying the 1911 with hammer down on a loaded chamber. Results proved it was almost impossible for the pistol to go off if dropped no matter what the angle, at least so long as ammo with milspec primers was used.
They actually found that the firing pin was more likely to dent a primer if the pistol was dropped in the cocked and locked condition.
With no endplay the firing pin could not build up speed and inertia, with endplay the added movement allowed more inertia.
The instructions in the manual are for times when the pistol may not be in your personal control at all times, and on the range.
The Manual, which is a Calvary manual, presumes the presence of the issue flap holster.
A friend witnessed an AD resulting in death due to a guard not knowing that someone else had loaded the pistol before is was passed to him when he came on duty. The pistol went off in the holster when being passed to the next guard as he came on duty. Why it went off is unknown. Had he opened the flap he would have seen it was cocked, but apparently no longer locked.
If you carry the pistol fully loaded, seven in the magazine +one in the chamber then you'll either carry cocked and locked, which is fine if carried in the issue flap holster, or with hammer down on a loaded chamber.
Since the flap holster may not always be available, and certain situations may call for putting the pistol down for a moment or tucking it in a waist band so both hands are free, lowering the hammer would be an option.
I think they use the term "tactical reload" these days, inserting a fresh magazine while theres still a round in the chamber rather than shooting till dry.
The flap holster also prevents mud, gravel, or bits of clothing from getting wedged between hammer and frame or slide. A lowered hammer also prevents stuff from getting in.
A lowered hammer is also far less likely to become bent if the pistol is dropped or the owner takes a hard fall.
Grip safeties can become wedged in the down position by rust, hardened fouling, or debris, and more than once I've removed a 1911 from a civilian type open top holster and found the safety was no longer engaged though it had been engaged when the pistol was placed in the holster.
AD from troops picking up rusty handguns and rifles from the field days or weeks after a battle were enough of a problem that officers were told to instruct their men to leave any U S firearm they found abandoned where it was, so a squad trained in retrieving such weapons could deal with it.
The redesign of the S&W revolver passive hammerblock came about because of one such incident involving a Britis .455 Hand Ejector picked up two weeks after the owner had fallen in battle.
Milspec handguns are not expected to receive tender loving care, or even a cursory cleaning during months in the field.
Many soldiers only carried a handgun because the previous owner was shot dead a few feet from them and they quickly retrieved the weapon for their own use.
I've cleaned up old handguns found in drawers or nightstands years after the owner died, looking fine on the outside but with internals frozen solid by congealed grease and/or rust. Almost every one of those pistols brought to me was still fully loaded, and the person who found it did not know enough about pistols to check it.
There are a million reasons why any mechanical safety device can fail, and only one reason why they don't fail, that reason is dilligence in all aspects of its care.
The reason for the change to the exposed hammer was so that the hammer could be manually cocked for a more accurate and aimed single action shot if desired.
That too, but enclosed hammer and striker fired pistols were not particularly liked for serious combat pistols. A lot of people don't like the Glock for that reason. Not being able to visually check the condition of the hammer puts a seed of doubt in the mind of the man carrying it.
With an exposed hammer you can also easily check whether the firing pin moves freely.
Having vital moving parts hidden and inaccessible removes some of the feeling of control.
I carried a 1911A1 for many years, its one of my favorite handguns, I still have my 1918 marked flap holster and magazine pouches. I only stopped carrying the 1911 because an injury made it difficult to depress the grip safety and squeeze the trigger properly. The injury has healed as much as it ever will, but I still have a problem with grip safeties.
Also this just occurred to me.
When unloading a 1911 that is in cocked and locked condition, you have to disengage the safety in order to retract the slide. So when clearing the chamber you are holding a cocked pistol with safety disengaged. You'd also have to hold the grip firmly which would depress the grip safety.
If unloading a 1911 that has been carried with hammer down on an empty chamber, the slide is already free to retract and the hammer is in the not cocked position till the chamber has been cleared.
If a 1911 is dropped or thrown to impact muzzle first, the tilting barrel recoil operation means both the barrel and slide will be pushed back out of battery, with primer of a chambered round dropping in relation to the firing pin opening, and the recoil spring will absorb most of the impact.
If safety is engaged the barrel and slide will not move back, the primer remains centered to the firing pin, and the recoil spring can not absorb impact.
This would be another reason why pistols dropped while cocked and locked were more likely to show indentations of the primer.
If intended to never be carried with hammer down on a live round, there would have been no need to use the floating firing pin to begin with.
To top off this long winded presentation
An unaltered 1910 prototype, without any thumb safety at all.
A couple of these were altered by addition of experimental thumb safeties at the insistence of the Army.
Browning obviously had not considered the cocked and locked carry to be as safe as the hammer down on loaded chamber.