Im a new kayaker, but here is a snowboarding related story from back in the day. In the early 80's, when I started snowboarding on the east coast, many resorts required you to take a 'certification' run with 'the' snowboard guy, and then get a laminated card to prove you could ride 'in control' with the other skiers.
Man-o-man, if you got done with this and on the mountain by lunch, you were lucky.
Basically, my father taught me not to be an idiot. He taught me that the roads are slippery when wet, and if you fall into a fast moving river, you might die. I've done alot of 'risky' sports, downhill mtn. biking, ski/snowboard racing, skateboarding, rock climbing, etc., etc.
I know when I climb up a 1000 foot cliff face, I might fall. I know when I point my bike/skis/snowboard straight down the hill, I might hit a tree. I know now as I practice ferry-ing across the class I creek, I might flip over, suck up a bunch of wawa, and drown.
The natural selection comment is right on. Mix in a dose of regular bad luck, and pure bad timing, and anyone of us can go. We all know this. This is part of the draw, part of the fun.
I started off, ten years ago, with a basic class, morning on the lake, eddy turns, and wet exits. I think your standard human is born knowing the basics of a wet exit. Get out of the boat! thats about it.
AS Im pinned underwater, in my last moments of life, I will not wish I had been certified, or blame society for not making me. Im gonna think about my friends and family and say a quick prayer. By the same token, I wont get too down when I hear 'tuber drowns whereever' or 'kayaker lost on blah blah blah'. This to me is just natural. We all get in our cars and shuttle to where ever. I would agrue that the drive to and fro is equally as risky as white water kayaking.
Also when it comes down to it, if you look at a river, and it looks like no problem to you... I say go for it. Heros and legends have been made by less.