I guess we could do something like:
<normal coverage> - <adjustment for risky behavior> + <adjustment for pro-social outcomes>
Motorcycle cops are an obvious subset of people who ride motorcycles. It isn’t an extension at all to include them in your logic.
ATVs might be more of an extension. But, I bet if we wanted to we could find all sorts of jobs that are more dangerous than motorcycle riding.
(Edit: just to be specific, you say we have to draw the line somewhere. Well, then where?)
I'd say it is worth looking at redrawing that based on the maximum effect achieved. Drugs would be at the top of this list, followed by motor vehicle use and unhealthy foods. There is probably not enough justification to go beyond the 3.
I guess I’ve been beating around the bush, but my point is that targeting drugs specifically for this sort of thing would seem kind of, I dunno, puritanical to me (as someone who doesn’t partake). I’d rather just insure everybody and hope they don’t hurt themselves, just out of their own self interest.
From personal experience, this is de-facto true regardless of what anyone thinks the law says.