If you sign a waiver taking all responsibility, and the method is intended to be non-fatal, you can do it. Take boxing, where a death in the ring would not necessarily result in a murder charge to the other party. Two fighters could make it hard to distinguish the intent to go beyond the bounds of mere injury.
OK then someone challenges you to a boxing match. His name is Mike Tyson. You have two choices. If you wall away how does that make you look to your kids? Or you accept and he kills you with one punch leaving your wife alone to raise your kids and your kids are left without a dad. How is that good?
I didn't say it was good. I said that under certain current circumstances it was legal. The point is that to some people it would be accepted, and they would only blame my foolishness, not Tyson's intent if I accepted.
If Tyson were to challenge me, I have no problem declining, and I have no problem discussing it with my kids. OTOH, would he take me up on a challenge to take the physics GRE?