That one idiot is one in hundreds of thousands that are smart enough NOT to do that, let him learn his lesson on his own. If he's stupid enough to continue, let him. I couldn't care less about the one idiot who thinks revving to redline and immediately shutting off his car is a good idea.
Once you are done doing whatever racing, and have made it to a safe place to park, your engine and turbo are equally cooled to the point where you don't have to worry about them. If you're running some monsterous turbo that is only oil cooled, then you have to wait, but most modern turbos do NOT need this extended cool down time, nor do the engines.
People are stupid, if they beat their cars before they're properly warmed up, there's going to be issues, that's always the case, and I see it in the dozens of cars I hear pulling out of my complex just after starting up, and they have a lot of rattling and even knocking from the engine bay. But cooling down is something that these cars are designed to do WHILE being beaten, once you're done and parked (given at least 30 seconds to a minute), there's no reason to keep it running. NONE. Period.
BTW that guy you yourself are *****ing about is the guy who's paying you to rebuild his engine. Let him be stupid if he wants to, it's his ****ing money.
Like I said earlier, it's the warm up period you should be concerned with, not the cool down. Your engine is designed to take care of that for you, and unless you're stupid enough to rev it up and immediately kill it, you'll be fine.