isn't Ferguson the place where all the riots are happening because of the cop that shot the kid? and the same place where a gas station was looted and set on fire?
the intention of the tear gas in the video was to pretty much disperse any crowds, and it's mostly non-lethal. i'm guessing that law enforcement's had enough stuff with the riots and is trying to keep people spread and keep it from going any worse.
when you hear *BANG* *BANG* *POP* you run you don't loving film it and yell "this is what its like LIVING IN A POLICE STATE #OPPRESSED"
and again, tear gas is mostly non-lethal, cops aren't raising guns and firing at the peaceful protesters.