I think there's definitely a good cop- bad cop game going on with Richard's and Ben's interaction with Locke, but not necessarily because Ben holds an evil plan about bringing Locke down. I think that was the impression needed to be given to Locke and that's where Richard kicked in.
Locke's a character striving for inner will to realize his metamorphosis and moves only when confronted by other people's patronizing. That's the kick Locke needs to move, some sweet dose of 'positive' stress (depending on what you understand from 'positive')- otherwise his all-too-human fears and self-doubt gets him quickly (I'm a farmer Locke once said but hanging on to his fears means in a sense that he refuses to clear the land before cultivating it). Had Ben accepted Locke's failure to kill his father and let him come along anyways, Locke would have become only weaker, more angry and useless for himself, or for Others.
From the earliest flashbacks on, Locke showed that he's a guy that is desperate for approval and recognition from outside- not necessarily in a 'vain' sense but due to the lack of what would be his primary experience of bonding and approval: father-son relation. For the same reason lack of that approval and humiliation is often a better fuel for him than his own will. That's where Richard comes: if Locke can't bring himself to thinking that he's special enough to make the 'gesture', let's put him in a situation where he'll realize he's being told what he can't do ("he is not who we thought he was", "everyone makes mistakes" after Locke says that he thought he was special).
I am not sure whether it would mean anything to Ben if he were to find out that James killed Cooper-Sawyer and not Locke himself. Most likely he'll find out about it but he said "unless you carry your father's body on your back, don't bother" instead of saying "unless you kill your father..." What matters is that Locke saw that his torturer can be gotten rid of, one can and has to let go of old baggage, or come to terms with realizing how much it holds one down etc.. I think this was a lesson to be learned from James, or rather a rare
gift exchanged between James and Locke. Something I'll post more about in a more fitting thread later.
I'm not surprised that it was Richard Alpert playing the good cop here. I am a kind of viewer not always quick with details but rather into the allegories of the narrative. That's why I think there would no better character than a doctor named
Richard Alpert who approaches a character like Locke in the midst of his most inner confusion and starts an eye-opening dialog about the truth at the heart of things. What's with the name? Richard in the show is a medical expert of some kind (psych?) that's curiously around with tranquilizers or drugs of similar kind when Juliette's about to leave the Herarat building for her new job, Sawyer's being tricked with the Bunny Number 8 or when Cooper-Sawyer mentions his arrival in the Magic Box. The real Richard Alpert is one of the three researches involved in controversial LSD experiments that US military had great interest during the 1970s.
I am neither suggesting that the two are the same Alpert, nor that there's governments' involved, nor that Locke's been given acid 
Seriously.. It just grabbed my attention that the character sharing the name with a researcher of a psychedelic drug that's known to cause highly personal experiences and awakenings about one's depth, happens to be the same guy who gives the same kind of 'mind-altering' talk to Locke. Considering Locke's searching and finding a direction included digesting magical herbs in the sweat lounge earlier, I see his conversation with Alpert as another sign of the psychedelic kind of wisdom and inner-knowledge that Locke sometimes needs to find his purpose.