Definitely disrespectful, but I don't blame them. In fact, I might have participated with them if I was there. de Blasio earned this. He is partly to blame for creating a climate of hate and intolerance for law enforcement. He ran for office on an anti-cop platform, blamed the Garner death on "centuries of racism," and told the world that he teaches his son to be afraid of cops. He shouldn't be surprised when his actions, combined with the protestors and race agitators, creates an environment that helps motivate someone to commit an act of violence.
IMO, this is a form of peaceful protest.