Not even extreme sports. Football, skiing, golf, jogging -- they all have dangers and people have suffered from accidents or repetitive stress injuries. Of course, sitting at home safe in your Lazyboy has its own health risks. Or driving -- that is probably one of the most dangerous things we do.
All of these people saying "I shouldn't have to pay for ...." fundamentally fail to understand that insurance about spreading risk, not concentrating it. Besides, there are risks in everything one does, and even risks in things one chooses not not to do -- attempting to fully regulate that through insurance coverage would mean everyone would be excluded for one reason or another, and only the extremely wealthy would be able to be fully free. Alternatively, by partially regulating activities -- choosing which risks to accept and which to exclude -- that is just a way for the powerful to exert control over those who have less power. Finally, there are financial costs to exclusion -- lawsuits and such. Any time litigation ensues between insurers (*) about who should pay, that is a pure unmitigated waste of resources. Better to just accept that through insurance, you might contribute a dime to a cause you don't like, but in all likelihood, someone else is going to contribute a dime to you for a reason he/she doesn't like. In the end, over hundreds of millions of people, it's a wash, and cheaper to just accept it than bitch and litigate and regulate.
(*) This could be Ins. Co. v. Individual Person (consider the individual a potential self-insurer)