What some people don't grasp is that, at those speeds, the other traffic won't even see you coming up behind them. Somebody doing say 120 will pull out to pass a truck, because the passing lane is clear. Except buddy doing 250 km/h suddenly appears in the back seat. At those speeds, by the time the existing traffic is aware of your approach, you're already there.
I really don't care if he kills himself, that's no matter to me. It's what happens to the innocent people around him that is the issue. He's endangering other lives, and that's the issue.