You can't charge someone for what ifs.
which is exactly why he is not being charged for a collision or with the deaths of several children in the backseat. rather, he'll probably be charged for what he did do.
regardless of whether he actually hurt someone, laws are laws, and they are there to be obeyed. imagine someone sitting around on yonge street with a rifle popping bottles off a mailbox down the street. maybe he hits someone maybe he doesnt. maybe the bullet misses your kid as you walk by, maybe a shard of glass flies by your face. sure, the guy never hurt anyone that day, but does that give him the right to act dangerously in a public place? should he be stopped from doing so?
at high speeds there are too many factors at play. 300 kn/h is 83m/s... in the time it takes you to say "one" you would be 83 meters from where you are now. IF anything came out from teh side of the road, IF something rolled out from under a car, he would have been out of control a danger to others, and all because he was going too fast to react.
speed limits are there to give us reaction times. school zones are so low because we are supposed to have a lot of time to be able to stop when jimmy runs out after his ball. not so that you can cruise slowly by showing off your shiny new ride.
many of the laws we have are based on IF situations. thats the whole point of a speed limit, IF you are breaching it, then you wont adequately react.
bottom line, you know the rules, you play the game, you take the risk when you break them, if you get then you're paying the price. in the end, its a game you chose to play.