Usually people that don't deserve it get thrown under the bus, not people that lack the understanding of the boundaries of their position, or show absolutely horrible judgment. Other ways exist by which he could "protect" (dubious choice of word for all this) his daughter than what he did - the fact that he didn't shows he's got no discipline. So firing him isn't exactly unwarranted. Cops don't fake arresting people. If there was a crime involving his daughter, then have the boy arrested by another officer.
Why does how the boy reacted matter in all this ? If he roughed up the officer, well he'd be in jail (or probably shot/tasered, heh). As much as cops do get away with it, they can't handcuff, threaten or rough up someone because they sassed you (case in Montreal was funny of a lady arrested for telling a cop to F off, heh). Then again, police in most places seem to not understand what escalation is, end up having to show that they do, indeed, have balls all the time, etc.
The cop screwed the pooch hard on this, they want to be looked up to and respected, well better hold them to an impeccable standard, no ?