People with heart complications can suffer from roller coasters, as signs posted around roller coaster point out. I've gotten quite a few bruises from riding roller coasters, even with all the safety equipment on. You often hear about roller coasters malfunctioning and then the people on them having to be rescued, and sometimes they fall apart/break which causes injuries. While most are safe, some are not.
Yes, for a person in less than excellent health, roller coasters can be dangerous. In addition to making a person's organs float, roller coasters elevate blood pressure from the excitement, and depending on the ride design, corkscrew features can cause nausea and vomiting, while sudden jerks can play havoc on the spinal cord, causing headaches or injury.
After constructing a rollercoaster, many precautions are taken to ensure that the roller coaster is safe for the public. If their are any potential safety issues, it would be fixed before it opens as a new ride. In addition, height restrictions are put into place, so there is no possible chance for the person to fall our. So, even though its speed and acceleration might be fast, it still is perfectly safe.
When used in moderation, most roller coasters are perfectly safe. Spending a few minutes on the ride is nothing more than a thrill. The most severe threat a person faces on a roller coaster is malfunction. As long as the ride is in good working order, there should be no concerns.
No, roller coasters aren't that dangerous. I've ridden them hundreds of times. I'm in my fifties, and I'm not afraid of the ones that are well designed, constructed correctly, maintained rigorously, and checked constantly to ensure safety. These rides are designed to work well and not hurt people. They are no more dangerous than hurtling through space in a rocket or speeding along on a bullet train.
Theme park rides are incredibly safe. Millions of riders experience them every year, and serious accidents and injuries are very rare. Still, rides doexert some extraordinary forces on our bodies, causing some really strange things to happen. It's the feeling of experiencing these sensations on our bodies that actually makes riding theme park attractions so fun - and the designers and engineers that create them are very careful to ensure that the forces placed on our bodies are kept within safe limits.