Let's put this into perspective, 2.9 million people die every year in the USA, 300,000 of those die from coronary heart disease. Every man and his dog is online now. The chance of someone actually coming to your house and doing anything is almost zero. Yes, some nutter killed someone but that's like saying you're refusing to go outside because you might get hit by a meteorite. If you were a well-known YouTube star or the guy had your personal details, then the risk goes up considerably but the way I see it, every day the window of acceptable speech gets smaller and smaller because people get more and more offended. Should the guy have made threats, no. Should he get more than a message reprimanding him and reminding him it is not acceptable to say things like that... again, in my opinion: no.
Piss of the idiots online and walk down the street with confidence that the bus is more likely to kill you when you cross the street, than the guy who thought you were crap at the game and cost him his ranking XD