Not sure if it's outdated or not
I collect 'art deco' .32 ACP or 7.65mm (depending on one's schooling) pistols. I don't have quite as many as IBMikey, but my current collection is thirteen. (I suppose with that number I may have to buy more...) I enjoy them on the basis of their historical significance and the engineering involved.
I don't think of them as substantial 'stoppers' in the modern accepted sense. They don't have a great deal of kinetic energy or momentum. (My normal carry gun is a .45 ACP. The smallest gun I normally carry is a pair of 2 inch M&Ps in .38 Special loaded with heavy-duty wadcutters.) What the 7.65mm pistols do have is low recoil and much under appreciated accuracy. I test all the pistols I own. They will all register two to three inch groups at 15 yards - that's minute of schnoz, not minute of head. (Yes, I am aware of movement and the dynamics of an armed encounter; I'm discussing the inherent accuracy of the weapon system. Nor is that statement meant as a general tactic for such difficulties.)
Modern medicine has removed much of the fear factor from being shot. Whereas I agree with BarnBWT, in that I would never consider shooting someone expecting them to expire in a few day's time from 'complications'. However, back in the old days, it was probably on the mind of the shootee. Getting shot with anything was a serious matter, long term.
Another consideration is the effective penetration of the standard round. A 7.65mm round of 6 grams mass is an effective penetrator. A properly aimed round will penetrate to vitals and cause damage. (Which is not to say a 9mm, .40 or .45 caliber won't penetrate better and do more damage.)
When the time comes my .38 Special revolvers generate more recoil than I can tolerate, I consider the humble .32 ACP - probably in a model M Colt or 1935 Beretta - will have to do.
A note about really 'tiny' pistols. Bill DeShivs mentioned the possibility of building a .25 ACP in a "...tiny, very flat and very lightweight" pistol. I am certain he is correct. However, the problem would be similar to that of a calculator build into a watch: How does one hold and operate the device? Aside from the perceived recoil aspect (a thin, light pistol would tend to gouge the shooting hand), how does one aim and fire the device accurately?
Just a consideration.