Stopping or killing a BG is not the only reasons for using hollow point ammo. Consider the recent shooting by the NYCPD in front of the Empire State building. (According to current reports ) Six of the sixteen rounds fired by the officers missed the BG and struck hard objects behind the BG. They did not ricochet like FMJ would probably do, instead they fragmented and the people hit by the fragments were not seriously injured. Had the bullets held together and ricocheted they could quite possibly have killed or seriously an innocent bystander, even one many blocks away. Bullet fragments are very much like small rounds of bird pellets, they don't travel very far and lose their velocity very quickly.
Also, way back in 1981 when Pope John Paul II was shot the assailant used FMJ 9mmP ammo. Several rounds went completely through the Pope striking people in his rear. That would be a very bad thing to happen in any self defense shooting by police or civilians. FMJ bullets, especially 9mmP, is known for through and through wounds in people.
To summarize, two good reasons to use good quality hollow point bullets that perform as advertised is to reduce the risk of innocents being killed or injured by ricocheting bullets or bullets that over penetrate the BG.
Also, way back in 1981 when Pope John Paul II was shot the assailant used FMJ 9mmP ammo. Several rounds went completely through the Pope striking people in his rear. That would be a very bad thing to happen in any self defense shooting by police or civilians. FMJ bullets, especially 9mmP, is known for through and through wounds in people.
To summarize, two good reasons to use good quality hollow point bullets that perform as advertised is to reduce the risk of innocents being killed or injured by ricocheting bullets or bullets that over penetrate the BG.