Just saw this tonight.
I agree that Kono was shown being needlessly abusive in this episode, especially to the poor guy honking at her for sitting at a green light.
Mike's idea that her punching the guy's windshield out should have been a dream/fantasy sequence. Maybe Lenkov should hire him to write/edit!
Kono allowing the bad guy to fight her with a knife was foolish by all stretches of the imagination. Again, this could have been written better, to where they somehow end up in hand-to-hand combat without Kono making it intentional.
I wasn't bothered by McGarrett letting Kono beat the guy up at the end. While this was indeed a violation of his rights, it was made clear to the viewer that this guy was both guilty and a horrible scumbag, so it was still satisfying to see him beaten like that.
I also wasn't bothered by Kono's speech to the "house mother", threatening to have other criminals beat her up while she was in jail if she didn't cooperate. Whether she was bluffing or not, this goes along with the "immunity and means" theme of the show, and it was for a good purpose (to force the woman to give up the location of the kidnapped girls).
A very similar episode ran on another CBS show, the short-lived "Vegas", during the 2012-13 season. That show's sex trafficking episode also featured an elusive pimp who kidnapped young girls and forced them into prostitution, who was finally tracked down at the end and beaten up by one of the cops.