I agree - this makes me physically sick.
We have no clue what happened prior to the start of the video, nor how any of this started. But regardless of who the initial aggressor was, I'll be darned if I'll let anyone get attacked and killed in front of me or my family without at least trying to do something.
If you've ever watched the show "I Survived..." a common theme is how often horrible things happen without anyone nearby so much as calling the cops. Truly sickening.
"Laws that forbid the carrying of arms... disarm only those who are neither inclined nor determined to commit crimes." - Thomas Jefferson's "Commonplace Book," 1774-1776, quoting from On Crimes and Punishment, by criminologist Cesare Beccaria, 1764