Come on, walking up to somebody you've penned up (for not moving?!), macing them, and walking away? Of course it's indefensible. And it's not fair to the officers trying to deal with the situation... the officers who were dealing with the situation, acting professionally in a stressful situation.
This guy had a very bad day at the office. But if that's the worst thing he's done in 30 years, it doesn't mean he should lose his job. Nobody died. Still, a little contrition, an apology, and a departmental reprimand are indeed in order! Maybe he should think about retiring; perhaps policing has changed a little faster than he's been able to keep up with.
I also find it funny that "blocking traffic" (except when it's done by the police) is somehow such a horrible offense and justification. It's not like traffic flows that well anyway. Causing a traffic jam? Not good. But so what? Traffic jams happens. Certainly in Manhattan. If it mattered so much, we should ban the president from visiting, police funerals, and the entire United Nations general assembly.
But what do I know? I'm thousands of miles away, in England, closer to deer and pheasants than protesters.