You missed my point AH. It isn't the issue whether there is a measure upon which one can say that the law was kept to or broken, it is about the difference between laws that enforce that which is clearly morally wrong (thus few if any in society having argument against them) and those that are set up because someone thinks they should be there in the form they decide (and which many in society might disagree with). I suggest these are clearly different issues/laws, different categories; and whilst all morality is from debate and agreement, it is not reasonable to take that to the extreme and say that because everything is ultimately someone's decision that all the laws hold the same status.
In the case of speeding one may be able to measure compliance or otherwise, but that does not mean speeding is always wrong. Laws can be wrong if they are either inherently bad laws, or if insufficiently defined to allow for different actions in different circumstances. Take the obvious example of someone rushing to drive someone to hospital before it is too late. But in many cases, including the example I first gave, the law passed is simply wrong to start with. But for exceptional circumstances, 20mph limits are just to boost control freaks egos, those who want to be responsible for making life difficult for others. I've heard no other valid argument for them. (Plus I suspect it gives the police an excuse to not get on with important crime fighting and bump up their record of prosecutions by grabbing fruit deliberately hung low for the purpose.)