I think opinions on Ouija boards vary so much due to religious backgrounds, personal experience etc. From a metaphysical standpoint a Ouija board can be used as a tool for channeling otherworldly spirits, beings, whatever you want to call them. Much the way a medium channels information from the dead, a Ouija board is a tool. Like John Edwards is a medium so *he* is the tool. Like a psychic uses tarot cards or a palm as a tool. Are they harmless fun in the hands of teenagers who don't know what the heck they are doing? Yes, most of the time. Can they be misused, of course they can. Is there real danger to them? In my opinion and experience there can be. I do not take them lightly. You are opening a channel in an unprotected way, in my background to do such work we would usually put up sacred space to protect ourselves. I would never channel any energy that I am unfamiliar with not even through a board. Most kids just sit down and call in anything that is listening. That can be good or bad.
The short answer is, would I give one to a teenager and turn them loose? No. Is it calling up the devil? No, it's calling in any loose energy hanging around and trying to communicate with it. More often than not it will be harmless, but who wants to take that chance? I think the biggest problem with them is that people do not know how to dismiss what they have called in and then it hangs around. I have cleaned up more messes from situations like this-I have about a hundred or so stories. Many of them that start with, "well we played with a Ouija board at a slumber party...'
Again, like I said, people's opinions vary greatly and to buy into what I have said you would have to believe in ghosts/spirits etc.