Never having served in the military, in combat, or on a police force, and having never killed a human being, I can't offer any meaningful first-hand opinion relative to defence against human assailants.
That said, I have had to face the sad necessity of destroying some potentially dangerous animals, and was able to 'get by' with a .22.......but that was after having practiced and practiced with the .22, so that I was able to place the small projectile in a suitably vital area for a 'humane kill'.
I've fired on enough variety of objects with the .38, and observed the effective striking power of a hot +P round, that, should I ever have no choice but to fire on a human assailant, I really do believe that the result would be grimly fatal for the assailant.......a necessary tragedy, if I'd no choice but to preserve my own life by destroying a human being, but tragedy all the same.
Hopefully, I shall never need to face such a situation, but I do keep a .38, loaded with +P rounds, near to hand, lest such a situation should happen.
There is one possible situation for which I suspect the .38 could well be quite inadequate. We commonly visit friends in areas where wild pigs are common, some herds of which are led by large boars, which have been known to attack humans.
Whenever we are in areas which the pigs may consider 'their territory', I carry my old 'pet' Smith M58, the .41 mag, with rounds I've made up to be.....in theory at least.....the greatest possible short-range shocking power, short of losing the cylinder from over-pressure.
In some improvised tests on various objects, my .41 rounds seem to have roughly the same close-range shocking power as .44 mag factory rounds. The truth is, I really don't know whether the .41 would reliably stop one of those big pigs.....I do hope I don't have to find out by experience.......it would be exceedingly disappointing to have the boar fall dead, but only after he'd chewed me into shreds.
One of our friends suggested that I really should 'play safe' by investing in a .454 Casull......and maybe he's right.....but I just like the 'feel' of the M58, and have a lot of practice time in with it.
cheers
Carla