The "policing" (using your term) done here is completely voluntary by people who don't want to see plagiarist get rewarded at the expense of the journalist. It's not something any of us want to do, but feel it should be done to send a message to others that they will not be rewarded for this practice on Steemit. Hopefully it will deter it from ever being done in the future so that no one has to hunt these post down and take time out of their schedule to downvote and post why they downvoted.
Some members are looking into a plagiarism API, but it cost money. So in the meantime some of us have chosen to do it manually. It's not organized, we simply choose to talk to each other and point out repeat abusers on slack when we feel like it. Lately, I don't feel like it and others have come along to fill in, because they want to apparently.