First off, I carry a .380 sometimes. And I fully trust every grown-up to decide what's best for his/her own carry based on his/her individual circumstances/requirements.
Years ago in the early online caliber wars, I coined the signature line "Shot placement is king; adequate penetration is queen; everything else is just angels dancing on the heads of pins." The first question, accordingly, is can you
hit the vital areas (heart/aorta, brain/spinal cord)
with your gun and ammo at the quick speed necessary? (A related question is, do you know where these structures
are in a human attacker?
Gray's Anatomy can be found online and is worth a study:
Gray, Henry. 1918. Anatomy of the Human Body .) And then let's look at adequacy of penetration to
damage those structures (a bullet that won't penetrate to the vitals is not going to suffice) . . . and only then should we think about energy, expansion, etc.
My friend Mas (who is kind enough to not give me grief for doing so, myself) says, "Friends don't let friends carry mouse guns." I've thought about this quite a bit, because when Mas says something, he's got a hell of a lot of research and experience behind his statement. Which got me thinking about the whole "mousegun" thing.
Mas certainly has a point in this particular statement. First of all, unless you're a pretty skilled/experienced shooter, small guns are difficult to work - their size makes them hard to shoot accurately with even the minimal recoil of the light rounds they launch (and accurate shooting is
crucial for the shot placement necessary for adequate penetration with light rounds) and they don't always function as well as larger guns. And the rounds themselves aren't as reliably effective: I've worked on three separate shooting cases in which .380 JHPs failed to adequately penetrate. On the other hand, I've worked on so many cases in which a .380 was used quite effectively - I've never seen a case in which .380 ball failed to penetrate adequately.
Based on the shooting cases I've worked on, I believe that .380s (and .32 ACPs, FWIW) can be adequately penetrative to get to "the good stuff" if ball ammo is used. I
don't trust these calibers to penetrate adequately with JHP rounds - and gel tests confirm that no .32 or .380 JHP presently on the market will meet FBI penetration protocols.
Naturally, the performance of your ammo in your gun is what's at issue. I (personally) carry ball in .380 or .32 ACP. I'm not weighing in here on whether ball ammo is a good idea from an overpenetration standpoint - I've worked on one case in which .380 ball overpenetrated the leg of the intended target and shot another person beyond him . . . but the leg probably isn't where an expert will be aiming, is it?