This thread is, well ... - just rambling.
Yeah, if someone was being beaten, I would try to do something.
What does that mean? Have done a lot of FOF, I think that is frankly naive to post.
Ok, here's what I would run in a FOF.
1. Two guys are kicking the crap out of a guy on the ground.
2. They are surrounded by a group cheering them on.
3. You arrive with your EDC - let's say a semi with two hi-cap mags on your belt.
A. You yell at them : They yell back at you (seen this, BTW).
B. NOW what :
1. Open fire?
2. At whom? The yellers? Through the crowd at the beaters?
3. The yellers turn to you and say : Hey, tough guy you going to shoot? Well, grasshopper - what's your legal justification for that?
4. Sure, they will flee in panic from manly you - or maybe not?
5. Going to hose a large group (prison time) - you will only shoot the BGs and not just spectators. Right.
6. Wave your gun around and don't fire? Well, it's multiple Tueller drill time. Think some won't get to you if they aren't so scared of you. Then you are shot. Mobs have taken down lone armed police.
7. Fire in the air - great plan.
So if you say, you gotta do something - think it through. Unless it is a loved one or you are ready for truly severe personal consequences for trying to save this victim - call the law from safety.
If you say you can't live with yourself, that is also internet BS. People have come through personal horror and many can live with themselves now - appropriate therapies can help.