In at least a couple of provinces in Canada (and I would expect in other jurisdictions too) there are at least 2 laws governing speed, and the one that wins in court is not necessarily the maximum speed law. I cannot cite chapter and verse but there are folks who've been ticketed for misuse of the passing lane when said drivers were going the posted maximum speed while traffic backed up behind them. Recently there has been a police campaign (I forget in which province) to warn and ticket drivers who use the left lane for other than passing. Even if going the speed limit. It would seem that blocking traffic is more illegal than speeding. That said, if you decide to speed and then have an accident, of course the law will be against you.
Conclusion: There is no perfect way to balance practicality with safety and with the vagaries of human nature.