I'm probably one of the last supporters of the .32 Auto. FMJ loads out of pocket pistols get 13"+ of penetration consistently, and aren't shot placement and penetration
the most important things in a defensive shooting? Given the FBI recommends 12" of penetration for handguns, a .32 Auto slug will kill someone just as dead as a 9mm, .40 S&W or .45 Auto if you learn to shoot it.
Another unpopular opinion I hold is that .45 Auto sucks somethin' awful out of short barrels. Velocity, energy and penetration plummet and reliability (in most subcompact .45 Auto platforms) suffers. You lose capacity and gain absolutely ****-all sticking .45 Auto in a tiny gun where a higher pressure, faster-burning cartridge like 9x19mm, .40 S&W or .357 SIG works just fine.
That brings me to my last point. .357 SIG is an absolute godsend to the subcompact auto market. A standard defensive 125gr .357 load performs identically to .357 Magnum out of those 2" snub revolvers that are so popular. Due to the faster-burning powder in the .357 SIG it also wastes less power and results in less recoil and report while getting the same results.
Let's use a Glock 33 are our auto example, eh? A G33 is about the same size as a snub-nosed .357 Mag J-frame or SP101, but lighter, and packs double the capacity (9+1 vs 5). So you have a lighter weapon of practically the same size with double the capacity, the same ballistic performance, and less recoil, noise and flash.
Here are some links regarding ballistic data for the .357 SIG and .357 Mag: