There are steep drops that make you feel like you will fall out of your seat and there are turns that cause you to dangle upside down. There are a couple of reasons people do this. But most aren't. You get on the roller coaster because you trust the manufacturer. You know that amusement rides are very carefully regulated.
Safety is the number one priority.
You believe that no matter how wild the ride is, you will be safe because the manufacturer built the ride with safety as a first priority. Second, you trust the restraints that are provided. You trust the harness or the bar that holds you in. That's always the first thing I check when I get onto one of these rides. I want to make sure my harness is fastened securely.