The people being pulled and "dragged" were resisting arrest. They refuse to move upon being arrested, which leads to them being forced to move. There is nothing wrong with what the officers did.
Um, you think there is nothing wrong with arresting people for peacefully protesting? Go check the Constitution, this country has an amendment called "Freedom of Speech, Press, Religion and Petition". It's the First Amendment, and its description is:
"Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the Government for a redress of grievances."
Therefore, people are allowed to protest without being arrested. By logic and reasoning, the cops did, in fact, do something wrong.
Let me explain once again: In the United States, the First Amendment, which is part of the Constitution, guarantees the right of free speech and peaceful assembly. New York, where the protests took place, is a part of the United States. Therefore, Federal laws apply to New York. The people in the videos were peacefully protesting, which is allowed by First Amendment (which I explained above), but were arrested. Hence, the arrests were wrong. And hence, the terrorists making the arrests did something wrong.
Understand?