Although we all break them, just like the Decalogue, the law is still the law and should be obeyed.
Plus, its fun to give you a hard time.
This brings up a number of interesting questions.
Unlike the Decalogue, small violations are not enforced. The issue of speed limits today brings up very fundamental questions about how we view the law, and what counts as law.
There are many philosophies of law, from various forms of legal positivism to natural law theory and many others - but almost all of them include some provision that, in order for something to be law, it must be enforced. That is, if something is on the books, but violations of it are known and unpunished, then we can at least question whether it is law at all.
Obvious examples include those silly laws that make it into trivia games like, "Did you know in Minneapolis it is illegal to pull a Radio Flyer down the sidewalk with a dog inside?" Or things like that. Is that actually against the law? Is it sin to do so?
These are interesting philosophical and legal questions. Are we responsible to know all of the thousands and thousands of laws we may inadvertently break in any given day? I am quite sure I break many laws, and probably commit a felony or two every now and then. Certainly, I do things that could carry some kind of non-negligible sentence.
If I knew what these violations were, I would stop. But I know there are so many laws I just have to be breaking some of them.
Combining all city, county, state and federal codes that touch every possible facet of our lives, how could we then live at all? We would be afraid to do anything, because we don't know for a fact that any particular action is legal. But we do have much better knowledge of what is enforced, and in practicality that is what we must go on.
I just wanted to point out that those questions exist, not really debate them. This whole discussion is not that relevant to me as a practical matter, but it's intellectually interesting. If a majority of persons break a certain law every day, and no realistic attempt is made to enforce any of these laws, are they law at all? If its penalties and enforcement are applied unevenly (and applied unevenly on purpose), is it law?
I drive the speed limit at all times, and I try never to roll through a stop sign. My main reason is not because these things are illegal, but because I have a very rational fear of anyone whose word, by itself, with no other evidence, can cost me a ton of trouble in time, money and annoyance. The man who pulls you over has absolute power over your fate in a ton of ways, with little or no check on that power, and I decide to avoid that sort of situation. That is not saying anything about the character of our officers. It's just a recognition that avoiding a person with that power is a good idea.