Actually, he did cover their motivations - didn't you read the article? The vast majority of them are spoiled suburban punks who are motivated by boredom and the search for some safe (i.e. the chances of NYPD cops actually using lethal force against demonstrators is zero) thrills.
When I was a boy, the college age punks spent their boredom on eating goldfish.
Of course, it was Depression (Big, Big "D") time and most couldn't afford much else. They tried to make Ripley's Believe It Or Not through the sheer number of the little carp they could eat at one time.
Then WW2 came along, and goldfish were mostly forgotten.
Well, maybe. That's certainly what the press keep telling us. Yet I can't help but wonder whether in amongst them there are people genuinely fed up with the growing intervention in their daily lives by faceless men who were never elected. Today in Australia we are facing yet more criticism from UN HR commissioner Mary Robinson, for instance. I never voted for her, or against her, yet apparently Australia is in breach of some international 'covenant on the rights of the child.' It reminds one of how the Founders must have felt early in the piece. (Supposedly) free men, yet still subject to rules from absentee authoritarians with no real understanding of the problems they're addressing.