this is such a wild take to me... it's impossible to quantity at what point something becomes a net negative for society. Smoking seems to be an obvious example, because it's addictive quality inhibits a fair decision to the smoker, and it's something with a lifelong pathology.
But trampolines and mountain biking are both activities that result in ephemeral injuries. There is the rare case where a particular injury might become chronic, but how is that a drain on society, and not primarily the individual?
by your logic, should we also ban (or require insurance?) for football (hand egg), boxing, martial arts, (Tai chi?), cars, religion, guns, knives, prescription medicine, children, leaving your house at all?
edit; I'm happy to steal more ideas from sibling comments! I already stole football, but now I want to add obesity, and all mental health conditions.
I'm really curious about the context the idea of net negative comes from, but I probably should also take a stab at a conclusion; why contrast individual actions and decisions in the context of society at all? The decision to do anything should stop at 1st order, and maybe 2nd order effects. That is to say, when trying to improve society, it's fair to look down into smoking and say, we should spend attention on fixing this. But it's incorrect to look at an individual decision "should I smoke" and weight it's effects on society. (How will this effect my family, or my environment is 2nd order, and should be accounted for)