I get the feeling neither Ben or Widmore are the "good" guys, they both want the island for their own reasons. Widmore said last season that "the island was mine and it will be again". And Ben didn't want to let go of the island to Locke in season 3 either. Locke was being played by both sides, and I hope he finally learns that neither of them can be trusted!
As for why Ben stopped Locke from committing suicide, he needed the info Locke told him (Sun/Jin, Eloise). Once he had it, he didn't need Locke anymore.
Does anyone else have the feeling that Locke's resurrection is what's preventing the injured people from being healed? Maybe Locke is soaking up all the healing energy just to stay alive?