Let me state at the top - I don't believe the crash of Oceanic 815 was intended. The business with Desmond just happening to not press the button at the precise moment that Oceanic 815 was travelling above the Island affords such an unlikely set of circumstances against someone intending that to happen it breaks my probability register.
So that's that.
And then I had other arguments about how the crash wasn't intended. Like how getting all those people deliberately on the plane requires such a level of organisation and planning it, once again, baffles me. All of it would have taken is for Hurley to choose to spend one more day with his father after they had made up to not go to Australia and not get on Oceanic 815, or for Kate not to help Ray Mullen (the one-armed farmer) so she wouldn't have got caught and been transported on Oceanic 815. (All the other characters have equally finely-balanced circumstances that could have changed.)
And then there was always the issue of survival. Namely: If you want to get a bunch of people onto a desert Island then sending them there in a large tube of metal and allowing that same tube to drop out of the sky and crash into the ground in flaming debris is not the best way of going about it. Let's just say if I wanted to get all my best friends to the Island for a party, a plane crash is not how I would make sure they arrived. Chances are, some - if not all - of my best friends wouldn't make it.
However, since Meet Kevin Johnson, and more acutely in Cabin Fever, there's been gathering substance to the idea that some people cannot be killed. Michael has a specific purpose and he cannot be killed. Locke, as Ben ruefully states, also cannot be killed (and so shooting him at the mass grave was pointless). If some people are "supposed" to do something, then they stay alive.
That's one aspect of my argument attacked. Approximately two hundred Oceanic 815 passengers were killed. They were not protected by this 'invulnerability'. Those that were protected - the likes of Locke, Jack, Hurley, Michael, etc - were guaranteed to survive. And that's my point. If the plane crash was intended, the invulnerability of the 'special' passengers guaranteed their safe arrival.
And what of the likes of Joanna - the girl that drowned during White Rabbit? She survived the crash, and yet pointlessly died not long after. To that I would argue that she was either not "supposed" to survive and yet did (and so course correction caught up with her and Joanna the strong swimmer died whilst swimming!), or her death was the purpose for her on the Island (it triggered Jack's accepting of the role of leader for the Oceanic Tribe). Looked at from any of those two perspectives, the deaths of passengers since the Oceanic crash can be explained.
Let me state at the bottom - I don't believe the crash of Oceanic 815 was intended, but one of my main arguments against it has been knocked over and who's to say my other arguments won't be equally disproved over the course of the show. . .? So I don't believe the crash of Oceanic 815 was intended, yet, but I'm more receptive to the idea that it might have been.