I'd guess that most "studies" are done only
after a 'problem' is discovered. It's hard enough to predict the future (as opposed to the past) without having to include all the problems that will come with it.
I'd also suggest that there have been several million people who have watched 3D without any problem(s). 24 people hardly makes a definitive group, after all they all probably live in California, which makes them suspect from the beginning!
IMHO, your poll has too few options; the only things that bothers me about 3D are the price$.
Finally, from what I hear/read 3D has yet to be found useful in 90% of its applications. And that 10% is mostly limited to medical instruction...