All or none

Roller coasters are a fun way for people to experience the adrenaline rush that so many people crave. They are precisely engineered to thrill riders without causing them injury. In order to accomplish this and remain safe, they are engineered to safely handle the majority of riders. This means that there are height and weight restrictions. People who fall outside of those norms will have issues being properly restrained by the ride's safety systems. This is why amputees are sometimes told they cannot ride, because the lack of limbs can cause them to fall out of roller coasters.

So we have amputees complaining that they should be able to ride roller coasters, while claiming that their rights under the ADA are being violated, and also complaining that they get injured when the ride isn't able to protect them. You can't expect the kids who staff these rides to be able to judge the ability to ride on a case by case basis- they aren't engineers or doctors.

Damned if you do, damned if you don't.