One where actual use has shown handgun ammo, even hollowpoints, performs like ball when it hits wall material (that means it keeps on going). That same world coincidentally sees personal defense ammo in .223 and 5.56 to be generally poor against barriers, as the round already has a tendency to fragment and many of those good defensive loads enhance fragmenting or spreading. That world also sees more law enforcement moving away from pistol caliber submachine guns for SWAT use towards 5.56 rifles, and it's not because of a sales pitch.
If you use M193 or M855 for personal defense, shame on you; folks who aren't limited by the Hague Convention aren't using them for a good reason. Any round good enough to stop a person carries the risk of going through most walls. The .223 and 5.56 simply carry a slightly reduced risk of doing so compared to most pistol rounds.