Yes, trampolines are potentially dangerous and you can in fact get hurt seriously on them. But so are the following: Swing sets (you can fall off the seat while swinging), bicycles (traffic accidents, wiping out), skateboards (you can fall off while going fast), rollerskates (you can fall while going at high speed), electric toys of all kinds (you can get electrocuted), the Game Boy (repetitive stress injury), running around (you can trip and fall, possibly getting seriously hurt), sleds (you can hit a tree, a rock, or a car at high speed), skis (falls and collisions), slides (you can fall off the top), climbing gyms and trees (you can fall from a height), marbles (a choking hazard), jacks (another choking hazard), swimming pools (drownings and hitting your head while diving), barbecue grills (the flash fires and blown propane tanks are threats), a pet (they can scratch or bite), pencil and paper (you can put out an eye on the pencil and choke on broken pieces of crayons), and just about every other thing you can think of.
This is just one thing we have to accept. Any parent has to decide whether any item provides enough benefit to justify the risk. If you have a zero tolerance for any sort of injury, you have no fun. This is no excuse for recklessness--trampoline risks can be cut if people use common sense and avoid horseplay while on the thing. But I cannot see having them banned totally, any more than I could see banning a swimming pool or riding a bike. Use common sense.
Incidently, trampolines are safer than going out in service. Service, with all the dogs, traffic hazards, bad steps, householders willing to shoot the Witnesses, and the stress, is far more dangerous. And there is no benefit of any kind--neither fun nor exercise--that can warrant the risk. Anyone who wants to legislate trampolines out of existence ought to start with the Witlesses.