They traded Chandler Jones because they could get a high pick for him and because they weren't going to be a league to afford to keep him the following year. The team didn't even suspend him after the synthetic marijuana incident.
Harmon clearly didn't put himself in jeopardy at all. All it did was cut his vacation very short. You're acting like the guy got busted with a hard drive full of kiddy porn in his suitcase, four AK-47s in a guitar case, and a brick of cocaine shoved up his rectum. This was literally far less of a big deal than the Gronk party cruise, except insofar as it might merit league discipline. He'll probably get one game at most like Blount in 2015. Oh yeah, remember that? It was the year Blount got suspended for riding with weed in Bell's car and when he was released by the Steelers, the Patriots immediately snapped him up. Guess Belichick was really upset.
I also regret to inform you he played very well in the playoffs and regular season. But yes the Patriots should definitely trade all their best players every time they lose a game because clearly this roster isn't cutting it.