Sado masochism is not of much interest to a lot of people. But there are others who do this and some other things that some might deem strange or scary. Still, we can allow them to do with their bodies as they will as long as they are not hurting someone else without that someone else's consent. Our bodies are used for many different reasons when we have freedom.
In America today, there are too many people telling us what we can and can't do. Next thing you know, it will be illegal to get piercings and tattoos. I believe that sado-masochism should be legalized. What people do to their own bodies is their own business. This should be legal as long as they don't commit suicide.