In a way, I respect that he's doing what he loves to do, and since we're all going to die someday, at least he's doing what he's passionate about.
On the other hand, I think he's showing a lot of disrespect to those around him who have helped him recover from what was and is a serious illness. I'm sure his family and friends want Don to be around as long as possible, but they also want him to be happy.
So in the end, his 'selfishness' wins out. But if he's being selfish, than how is anybody in the world who does something dangerous for their own desires any better or worse than Don?
I think I'd do the same damn thing. But if things go wrong, then pray that his family and friends will show him any more sympathy than they already have.