What if it’s just the water.
From the very beginning, at least when things started getting weird, the Losties have been consuming lots of water and the producers have made it a point to show them drinking water . . . er, I guess it would be lame but kind of funny if, in the end, it was the water i.e. something “in” the water causing massive group hallucinations.

It would be funny. My input on the waterbottles:
The ajira water bottle was the easiest clue for Ajira, seeing as water bottles are necessities.
And they need water to live.
Hahaha i’d love it if it turned out to be true. I can just see the writers sitting at home chuckling to each other at how easily they led the world on a wild goose chase.
I’m pretty sure there’d be a few angry folk who have spent hours researching time, black holes, family tree’s, the bible etc etc etc and all it comes down to is some kind of group acid trip. Wilma thankyou for making me laugh 🙂 hahaha
let me tell you from experience, people rarely hallucinate the same thing. and thats unfortunate. it would be more fun to hallucinate together. oh well.
It gets my vote for the best, simplest and most plausible explanation of all…
Why didn’t I think of it?
LOL!
yes but each could be hallucinating their own hallucinations plus being convinced of other’s hallucinations. The brain is very powerful but easily convinced. I haven’t done a lot of psychedlics but I have been able to “experience” things that my friends were “experiencing” after they convinced me of them. It would be funny if a rescue ship pulled up and the rescuers got out and found a bunch of survivors running around half naked, speaking gibberish of hatches, others, time travel, polar bears, smoke monsters . . .
all while drinking some kind of messed up water from a legitimate but abandoned research facility.