Ultimately I think the shooter has to go with his own level of confidence in his ability to function in a crisis. Personally, I have never had a malfunction because I improperly seated a magazine and before I carry any pistol, I know the magazine has been firmly seated as well as the functional status of the pistol being 100%.
Like I said before, in 33 years of shooting handguns I have never had a round go "click" that wasn't the result of a high seated primer where the first strike merely seats the primer without igniting it and in ALL cases where that has happened a second strike set the round off and I've never repositioned the round for second strike since combat pistols are designed to strike the center of the primer, hence the term "centerfire". I wish some fellow handloaders would chime in because the same issue applies to handloads. Rounds with high seated primers have and do escape the factory just as a worn priming tool will sometimes fail to seat a primer to its proper depth. A simple check would be to run your thumb over every primer in every round you load into your defensive pistol to make sure they are slightly below flush with the cartridge rim.
With the reliability of factory ammo it is not likely, but it's also not impossible to get a factory round that failed to get a powder charge. A primer generates enough force to push the bullet a fair distance into the bore. So the example of a shooter executing a lightning fast tap-rack-bang in competitive shooting is actually a poor example because more than one shooter has heard or experienced "click" because the round didn't have a powder charge and simply ejecting the empty case and chambering and then firing a fresh round into an obstructed bore is going to result in injury from minor to major and possibly death.
The statement about being a target with a pistol malfunction while your assailant proceeds to shoot you violates one of the basic rules of defense shooting where you failed to fire from cover. So if you don't possess the confidence that you can handle stress under fire, maybe an immediate course of action for you should be tap/rack. Speaking only for myself and using a SA/DA pistol, I'm going to immediately pull the hammer through for a second strike based on my experience where it's always worked. For those that carry a back-up piece that's a pretty sound decision. In that case if I did and didn't get ignition from a second strike, I would immediately go to the back-up pistol.
As far as instructors go, my first question to any of them would be, have you ever been in an actual gunfight? If they hadn't, I'd probably seek training elsewhere because I am already aware of most of the theory. Also, you might consider that tap/rack was born out of single action pistolcraft before DA autoloaders came into common usage. Most instructors advised against second strike because in an actual gunfight, clumsiness in attempting to pull the hammer back manually before firing again could result in a slip of the thumb. With a DA autoloader your finger is already on the trigger and since I'm convinced that there is a bout a 95% chance that you're going to get ignition on the second strike, I'll take those odds.