I once did some experimenting to see how fast I could get a PB flying, out of a cheaper $30 gun. I had it near 500fps before the bolt actually blew out of the gun. I have no doubt that a marbel shot out of it could be deadly.
I also have a full auto PB gun. Cost me $80, bought it right over EBAY. That thing is just as fun, and much cheaper, than a traditional firearm. BUT, I would never shoot it at anyone not playing, nor point it at anyone I wasn;t trying to shoot. I follow the four rules even with a PB gun, and have never had any problems.
I think the biggest problem is kids that don't have real firearms. They don;t understand the problems that they can cause, and being taught that it is acceptable to point a PB gun at people, I think they are more apt to cause the problems.