I don't condone violence. I think that the guy who threw the punch should have been punished (legally) if he caused any major damage. (it didn't seem like he did though)
However, those of you calling him a pussy for punching the white dude seem to forget something: this guy had no clue that this was a social experiment. He acted as a last resort, because he was fed up of the white dude not stopping the harassment. You gotta admit he pushed them all to the limit. You'll notice that towards the end he was even trying to grab the Muslim dude by the arm...
Bottomline is: these YouTube guys sometimes push their experiments a little too far, and sometimes shit gets real.
Reminds me of this one:
PUNCHED FOR FARTING (EXTENDED, RAW) - YouTube