So if I said "I think that Oceanic 815 took off from London", no one is allowed to point out that the show explicitly contradicts my opinion?
NO, that is not what I'm saying. It's been know since the beginning that the flight left Sydney. To argue that would be silly. It was specifically stated on the show. But, no one stated at exactly what point people died. As you pointed out, they died at different times. When and how wasn't specifically stated. These allows for interpretation.
The fact that Ben and Juliet are at the church is further evidence that they survived as these people did not meet the survivors until after the crash.
I disagree. It's not evidence of survival. Yes they met after the crash. But they all met on the island. I'm suggesting that they were dead when they met on the island. Is goofy as it sounds, they all died at different times, and met at this point as part of the test.
No bodies, either, so the plane must have been empty and flown by an artificial intelligence which imagined this story of survivors to keep itself occupied until its batteries ran out and it died. 
I would think the bodies would be on the plane, still strapped in their seats. I'm no expert on airline crashes. (And never hope to be.)
Take it easy, no one is being the the thought police. This is a discussion board. People try to sway opinions with arguments. No one said you have to believe what they do or get out. If you're not open to discussion about other possibilities then why bother posting? As you said, everyone is entitled to their opinion, and disagreeing with yours is no worse than you disagreeing with theirs.
That is my point. I'm suggesting another possibility. And the response I get is "you're wrong." I've never told anyone else they were wrong. In fact, I had the same theory as they did up until the credits. That's when I changed my mind. I'm not saying I'm right or wrong. It just my opinion.