After the series finale aired, many users started a revival of the "they all died in the plane crash" theory, or some such similar theory - I won't list them all here.
Most of these theories don't have specific evidence; theory-makers only seem to care that they fit with the facts, not that there's proof in the show for the theory. Critics of these theories will often point out that there doesn't appear to be any proof for the theories. Apologists point out that there doesn't appear to be any proof against their theory either. Critics can't seem to think of any proof that disproves the theory (or at least, proof that the theory-maker is satisfied with). Lots of arguing ensues. People get angry. It's the same thing every time.
I would like to highlight a specific point in these arguments. Both sides point out that the other is wrong due to lack of evidence. This is a logical fallacy, called an "Argument from Ignorance". The fact that it hasn't been proven false does not make a theory true. Neither does the fact that a theory hasn't been proven mean that it is false.
Allow me to illustrate my point. The next paragraph is a theory that I just came up with. I do not believe this theory to be true. That said, I have put together this theory specifically so that it's unprovable. Nobody will be able to actually prove or disprove my theory, no matter how hard they try. Here we go:
- Lost is about a group of people who died in a plane crash in 2009, we'll say. Everything that happens in Lost didn't necessarily happen, but is the collective subconsciouses of everyone on the plane exploring their pasts. As it turns out, Jack Shephard wasn't actually a spine surgeon during his life, but actually worked in a box company. John Locke was Jack's manager at this box company, but felt he never deserved the job. Kate was going to marry Jack but left him at the altar. All of these people lived in LA (a very significant city in the show) and often vacationed on Oahu. Their lives were often tied together in curious ways, but they never ended up on the Island together.
This theory can't be proven wrong, but that doesn't make it true. It doesn't make it untrue just because it can't be proven right either. So how do we differentiate between all the different equally valid theories and accept one? Occam's Razor. "The simplest explanation is usually the correct one". Occam's Razor isn't always right. But when we don't have anything else to work with, it's a good tool to use.
What's the simplest explanation, then? What you see is what you get. Whatever happened, happened, exactly as the show portrayed it to happen. It was all real.
I know some will disagree with this, but this is why I don't believe they died in the crash.