I respect both William and Cedric, as they have been performing this type magic for longer than me, so I would have to give in and say it is dangerous.
I personally have never had a bad experience with this effect, and with so many geek magic effects, if you practice and in this case do it slowly, then there is no chance you can hurt yourself.
I think, even if it is dangerous, telling people that it is dangerous is psychologically stopping them from doing the effect in case it does go wrong. I have never thought of this trick as either magic or dangerous, just something cool I can do that I have mangaged to get an 11 day gig out of.
If you want to do it then do it, and don't let people warn you off, but please at least consider what both William and Cedric have said, as even though telling you its dangerous is putting you off, they are at least letting you know that something CAN and WILL go wrong if performed without practise, practise and going slowly.
Simon_Magic