My point is that if you are speeding, you can lose control and hit someone else. You run the risk of having an accident that injures or kills someone who had no part in your decision to drive too fast. If you choose to swim in dangerous water, you aren't going to run off the road and kill someone who was just passing by on the way to Sunday School.
In the water, the rescuer endangers himself, albeit willingly and unselfishly, when he enters the water to rescue someone. Maybe he didn't get up that morning with plans to pull someone out of the water, but at some point he made a conscious decision to put himself in harm's way.