Is it really though? They have medical requirements before they can fight, a process is in place to prevent them from fighting if they are not up to it medically or skill-wise. They have a set of rules to ensure their safety, along with refs, doctors, and other commission members, along with their own team to ensure it is as safe as it can be and to stop the instant it is no longer safe. They know exactly who they are fighting and everything about that person, and exactly when, where, and they know that person is alone. There are scheduled breaks where they are examined for their own safety.
There are plenty of jobs that are more dangerous, to label a fighter as "putting their life on the line" is utter bullshit.