Because we can't prove consent when certain acts go wrong, maybe we should just ban acts that have the potential to cause serious harm.
If you engage in anything like that, and your partner gets hurt or killed then you are punished, consent is not relevant. It's the risk you take.
I am veering more and more towards this as the thread progresses. If people want to speed in their car, take coke or get into asphyxiation for kicks - they should know that they are doing something illegal. If they kill someone on their bike or by giving them coke or suffocating them, they should be up for manslaughter.
Acts which have a high likelihood of causing damage like anal fisting, burning or piercing the skin should not be legal.