I like to think that Jim wouldn't have done it even if Bruce had been a little more trusting.
I don't know. Jim's in about the most dubious place he's been, morally, in maybe his whole history there. He hadn't been a cop for more than a year. He was running a gang. A relatively benevolent one sure, but they weren't standing for law and order, there was no law. They didn't bring people in or worry about due process, they beat the tar out of or outright killed the Other Guys in order to drive them off. Jim was making deals with Two-Face and trying to claim territory and spending a huge chunk of the year not being able to trust Batman. And his wife just died, stupidly, for no reason, at the hands of the same guy who paralyzed his daughter, stupidly, for no reason (remember, Jim's the one who would have taken care of Babs during her recovery, so he knows exactly what the price was there). He's got nothing but reasons to do it and he's coming off twelve months being trained into a mindset that would see nothing wrong with it. As strong as Jim is, that still seems like too much to me.