I also suffer from terrible back pain and I know just how bad it can suck. It's not like the guy was racing while he's high. That would be idiotic/borderline suicidal considering the speeds these guys race at and I don't believe anyone (even a NASCAR driver) would be so stupid.
So lay off the guy and let him have his medicine! I'm sure there are plenty of NASCAR drivers that go out and drink themselves silly on a regular basis, but this guy can't smoke a little weed to help his pain? Fuck you NASCAR!