its plain and simple darwinism....
Cant say that I understand the relationship with your step son, I'm still young and lookin to start my own family, that said I would agree with most everything above. Timmy Duck put one hellova post up there for your wife to read. Show her the pics, show her movies of the stupid stunters and crashing from it. If his skills are that bad on dirt, for sure he will be dead in a short time on the street. And here is how it will happen (cuz I've seen it)
A group will go riding, mostly more experienced riders that he's managed to hook up with at some local bike night. They will expect that a kid on an R6 has some skills and let him ride with them. Someone will say "oh he's cool" and off they go. The ride will start off rather tame, maybe some stupid stunts in town (wheelies/stoppies)... maybe he'll wreck then or maybe he'll play it cool for a bit. Hope he wrecks then because later in the ride is when it will get ugly. Again, I was on this ride once...
After they get out of town a bit, they hit the country roads. Remember its night time....daarrkk country roads, twisting and turning, rolling hills. These are hard enough to handle during the day but at night, well we've been there. Trying not to get lost he's gonna try to keep up with the pack. Maybe make a stupid pass or two along the way. As the ride goes longer, the roads get a little more advanced. As the group takes off to rail the turns, he tries to keep up. First one, then another then a nice straight road. Looking down the road he sees markers that seem to go straight and thinks ok, things are calming down. These markers though are driveway markers and the road actually is a decreasing radius, heavily banked turn to the right. At most any speed above 40mph, this will get you knee on the ground. He of course doesnt see the other riders take the turn as they are way ahead of him. Instead he realizes at the last minute that its a driveway and tries to turn right. Doesnt counter steer, freaks out and winds up going into a tree..... he didnt live.
Now, as I said I was on this ride. Its like any other ride that typically happens on any given bike night. I happened to be riding at the tail of the pack on this ride....I saw the kid was making stupid mistakes and riding dangerously. I came up on the rider as he was taking out the tree, leading several other superbikes that were all afraid to ride with the kid.
Sux, but as I said, darwinism. We tried to help him, we tried to teach him, he didnt listen and just rode way beyond his skills.