Why the heck did Ben do what he did to Locke in "The Life & Death of Jeremy Bentham"

My thought was always that Locke needed to die "with his faith in tact". When he was about to hang himself he had completely được trao up and was convinced he was a failure. Ben came in and reassured him, made sure that he had regained his faith and knew that he was important and that he had work to do. It was only *after* this that Ben killed him (probably because he knew Locke had to die - I don't think he would have done it otherwise.) If not for this, why not just let Locke kill himself instead of murdering him and making it *look* like a suicide?

Cause he didn't need him anymore, after John told him about Faraday's mom. Also Ben still wants to be the leader on the island, but Locke is ment to be, so there was only one way for Ben

I think it's because he knew that in order to get back to the island, they needed the proxy for Jack's dad in the coffin.