Bottom line, a person...at least a wise one, carries what works best for them and what they have the most faith in. Yes, practice and reparatition makes for natural reaction. Buttttt, things can and do go wrong, manual safeties can and do fail, sweaty or dirty fingers do slip. If something like that happens you could, and most likely, will pay with your life. The less that can go wrong the less that will go wrong! Nor does everyone have the oportunity to put in the kind of practice you are talking about and practice under safe ideal conditions just don't count. Your key word is STRESS! The ONLY way you can truly practice for that situation is with someone coming at you with a weapon, or shooting at you and with a mutitude of disturbing things going on around you, in rain, sleet or snow, with less than clean dry hands, PERIOD! Even then the only way, and I mean the ONLY way, you'll know if you have presence of mind to flick that safety off is when you are faced with a situation where you have to. I simply prefer not to worry about a potential problem that I can completely remove before hand. Call it lazy, call it stupid if you wish, I call it the smart thing to do!
The point is that you CAN ,and many of us DO practice to the point where the intent to fire the gun instantly translates into taking the safety off and pulling the trigger. If you get to that point, then it just happens. You dont even think about it. Its like driving a car. Last year I was crossing an intersection that was right before a hill. Someone came through the red light and was about to broadside me. I downshifted,floored the accelerator,came to the top of the hill,realized there was a truck stopped just over it,hit the brakes,let off the brakes because I could feel the brakes about to lock up,judged the distance to the oncoming cars ,threw the car into the oncoming lane,steered out of the spin it was trying to go into from that fast of lane change on an icy road, decided whether i needed to put it in the ditch or or could get back to my lane before a head on collision,downshifted again,hit the accelerator looked in front of the truck to make sure it was clear,slid back into my lane and again steered out of the spin it tried to go into on the icy road. just in front of the truck,all in fraction of a second while my girlfriend was screaming and grabbing my left arm in terror. (makes it much harder to shift that way)
I didn't even realize what I had done until it was over. I was able to do that becuase when I was young and stupid and fearless I used to drive like a maniac,push my car to its limits and practice neat little tricks driving tricks. (A bootlegger reverse is fun to pull off on a deserted street,if you dont screw it up,hit the curb and roll your car,which I never did,but came damn close a few times,making for a "fun" afternoon of replacing suspension components) While I would not recommend it (In fact,I stopped because at one point I nearly ended up either dead by head on collision with a semi truck at 100mph or going airborne at 100mph into a ravine) my point is that practice makes even complex tasks under stress completely automatic. While I dont think I'm to that point with a gun,and I would not recommend the kind of dumb and reckless practice I got driving when I was younger and stupider,my point is that if you do it enough,you will get to the point where your dont think about it,like driving,it gets to the point where the intent to do something,like avoid a collision,is enough to make a complex series of actions happen.
Thats why I started reloading actually. I thought about it and realized that it took about 3000 rounds of 22 to become what I felt was reasonably proficient. If I wanted to actually get good,I would need even more. 22 is about 3 cents a round so that's about 90 dollars which is fine. For something like my 1911, that's 1000 dollars,just for what I considered a reasonable degree of proficiency.(actually,I realized it takes more than that,the 1911 is harder to use than a scoped 22,or maybe my 22 is easier to use) Another option might be to get a similar semi auto in 22 (that's on my list of guns I want actually)
I think its all a matter of what your used to and how much practice you have. I think if your dad put a 1911 or Browning High Power in your hand at 10 years old and you have been shooting just about every weekend for the next 40 years after that,your going to think "I need to take this guy down" and the rest is just going to happen. I also think its a good possibility that if you buy a 1911 and a box of ammo,and take it to the range in the back of the store,and shoot that one box of ammo,you may pull the trigger and be left thinking "Ok,nothing happened,lets see,magazine in,try the slide to chamber a new round,no it wont move,wait,safetys on" and as people have mentioned,by that time,you may be dead.
If your not going to practice,your probably better off with something without that safety. In that case,you better be aware of the other shortcomings of it.