If someone gets knocked out it could hold their head above water keeping them from drowning.(though it seems not in this case as head trauma was the COD)
I dont really blame the dad unless he was drunk, it sounds like a trajic accident.
However, I wouldnt be speeding with a kid unless the lake was uncrowded and smooth as glass, and only in deep water with no stumps.
I know that all sounds reasonable. But I would just hope to inject a little realistic perspective, that even good people take small risks from time to time, and it isn't reasonable to expect that to stop.
People like having fun, and sometimes that fun is in boats, and sometimes its done to thrill some kids. Most things that are fun involve some risk, and ~any~ risk means that in some statistically small number of cases it will end badly.
Unless we're going to try to purge ~all~ risk from life, then sometimes there will be sad stories.