First of all, glad to hear he's doing ok. Tell him to look up an online group to chat with while he's down, I joined a Harley Digest while I was recovering for 14 months. Helped keep my spirits up.
Now, as far as "Also, that motorcycles are dangerous!" so is taking a shower yet I recommend we all do it, frequently I might add. I would also recommend everyone learn to ride a motorcycle, it would make them all more aware of bikes in traffic, and that would inherently make motorcycles safer since 99% of all motorcycle accidents are the fault of the OTHER motor vehicle. Motorcycles aren't dangerous, cars are dangerous, and most people don't know how to drive them.
And if he's got it in his blood, you won't stop him. I spent 14 months in therapy and had to learn a new occupation due to a motorcycle accident. The day I got the settlement from the Other Vehicle's! insurance, I bought a new bike. After watching my head snap around every time I heard a bike go by for 14 months, my wife (girlfriend at the time) was not only happy to help pick it out, but put a down payment on it so the guy would hold it till the insurance check cleared. And she was the one who had to nurse me through the 14 months of recuperation and support me until I got a settlement.
So don't fight it. Be glad he doesn't take up sky diving or mountain climbing instead.
P.S. still riding 14 years later, and the now wife still loves to ride on the back.