The group views the flag as a symbol of oppression and the Disarm NYPD home page gives some background for their movement:
Racism and violence have been mainstays of the police since their inception, but in recent years awareness of the abhorrent behavior of the police—punctuated by the callous murders of unarmed black people—has incited rebellions all over the United States. The rebellions in Ferguson and beyond mark the genesis of a new political reality in America. The role of the police in poor communities cannot be obscured any longer. The police are a political/military entity bestowed with the authority to kill undesirable people with impunity. This is the reality of the situation. Disarm the NYPD will immediately act to end this reality. Disarm the NYPD has two immediate organizational goals. We will disarm the police of their guns and we will disarm them as a viable political/military entity in the neighborhoods they occupy
Their vision statement (below) sounds more like the now-defunct occupy movement than anything else:
Disarm the NYPD’s long term goal is the establishment of a new political and social reality in NYC. We intend to organize councils that will become the main political bodies in our communities. Instead of government representation, we would like to organize a political life in the city where people can collectively make decisions. With this arrangement, we intend to make the police obsolete.