Nah, I genuinely don't think Ben murdered 300 odd people in order to fake the wreckage. I'm not being defensive - I honestly don't see that being the case and it never even crossed my mind until I saw this thread. You can see my thoughts which I posted a few weeks ago
here, which shows that I did believe that Ben planted the wreckage, however he need not have had to kill anyone to do that.
I believe that he either had the money to acquire ready-made 'bodies', or more likely, he used the Casimir effect/teleportation/duplication thing that some of us discussed a few weeks ago - the basic premise being that one entity can be replicated and teleported to another part of the world - take the Polar bear in Tunisia, for example. I'm certain that this is how Dharma got a polar bear to the dessert. Ben even underlined this concept in last weeks episode, when he commented on Locke's rabbit dinner - "This didn't have a number on it, did it?" - Ben/Dharma painted numbers on rabbits so that they could tell them apart after they duplicated/replicated them - this was because if the two identical entities should ever meet it would cause a 'paradox' - something which was not "Supposed" to happen..something being in two places at once (or rather, the same place at once).
I feel that this is basically how Ben (or whoever, but i'm sticking to Ben) 'replicated' the plane wreckage - some form of Casimir-effect. I think he did it to protect the island and to keep people (i.e. Widmores of this world) off the scent. The real question for me is
WHEN (not if) he did this - did he do it pre-2005 or
after people got off the island. If it's the first option, then this indicates some foresight (powers of prediction) or plain old preparation for all of the possibilities.