The thing is, some people like full contact sports. And not just watching them but doing them. If you stripped tackles out of football or body checks out of ice hockey, that would make it a different sport, not just for the spectators but (much more importantly) for the athletes. Nobody makes it to a high level in a sport without actually wanting to do that particular one.

Full contact but restricted martial arts also exist and mitigate risks by limiting the range of allowed techniques. Some of them do it in different ways than others. Judo is full-contact but disallows strikes, which makes it massively different than something with strikes. Semi-contact karate avoids the full-contact part, which makes it different in a different way.

Full contact practically always comes with risks, and full contact with fewer restrictions comes at much greater ones. Spectator expectations or other parts of culture may encourage the athletes to take risks and go to greater lengths than they otherwise would. But it's difficult for me to agree that modern society should have no place for sports that mentally healthy people actually want to participate in just because it comes with a risk of physical injury or intentional roughness. If they wanted to participate in a different sport, they'd have options.

In the end it's of course a matter of where to draw the line. Rather few people would nowadays want to allow fights to the death even if the participants wanted that. (Although, in reality, I don't think such a sport would get that many willing and actually voluntary participants either.)