I kind of buy the "Door opening theory" as you called it. This board is more than a simple wood plank with letters on it.
I still believe that it should be relatively safe to play Ouija, as long as you play it properly and that you don't get in touch with an evil spirit. I agree that you can't decide what kind of spirit you'll contact though, so that's part of what bugs me here. I think that a lot of bad experiences took place because someone somewhere came to do something he/she wasn't supposed to. What do you think?
But, all of the above being said... If 3 or 4 of you guys came to me with a Ouija board right away in order to play... I'm not sure I'd do it now. When I played it many years ago, I didn't hear as much bad experiences and the likes as I did between then and now.