Only in the US are you likely to get sued if you round punches through the target and into a bystander.
Considering the odds, I'm usually but not always willing to take the chance. If I get into a shooting I'll probably get sued by somebody regardless of the circumstances.
As I pointed out, if the evil person has cover - or in an unlikely event, body armor, under penetration becomes a negative. I doubt that there is any perfect answer. Foresight and the likely environment where a shooting might occur should dictate ammunition choice. If one feels more secure carrying the latest in so called "high performance" ammunition that's what they should use. But ask yourself, "If I have to punch through something substantial to reach whoever is attacking me will this ammunition do it?"