Speeding, even a little, is a sin.

Is it as bad as murder or armed robbery? No, not normally. Doing 72 in a 70 mph zone is not going to be more dangerous than doing an even 70, by any reasonable metric. However, Caesar has set concrete limits, because limits of some sort do help to minimize injury and damage from vehicular incidents, and while it enables arguments about how taking traffic laws as strong suggestions can be sufficient, it also stops people from wasting the court's time with arguments like "I'm smart and fast enough to safely drive at 55 in school zones."

Declining to render unto Caesar by driving 72 in a 70 zone would only constitute a venial sin, of course. I've written about arguments I've had with people who would assert things like being momentarily inattentive to the speedometer whilst passing someone is morally identical to genocide, and how I think it's silly because whether or not marginal speeding is enough of a sin to warrant hell, refusing to distinguish between extinguishing numerous human lives and abstractly defying the social order in a trivial way is rather dismissive of the numerous humans and not at all helpful to the people who are, respectively, struggling with the particular sins and/or temptations to kill massively or drive quickly.

I suspect that this philosophy is also responsible for stimulating the opposite attitude, that certain things that are a little bad aren't really sins at all. I admit, it's the first rationalization that comes to mind when I'm sorely tempted to commit a venial sin (and sometimes mortal ones, but many of them are harder to rationalize), to save me from the fear of despair at having damned myself by succumbing to weakness and habit, but I do remember it's not that simple. I brought up speeding as an example because the first time I remember someone who still believed in sin write off minor things as not being sinful at all used speeding as his example.

I agree it's not very bad; most cops wouldn't pull you over for exceeding the limit by two miles per hour on a highway, and if one did, the penalty would be relatively light. Further, the limits are to an extent arbitrary; if we had sufficient mathematical models, we might find that 73 might be an optimal highway speed, after all, and 17 in a certain residential zone. However, we usually use round numbers because easy to remember and standard values make it easier for us to keep our eyes on the road instead of glued to the instrument panel.

I'm getting sidetracked. If bad sins get us into hell, then it does not follow that minor infractions aren't sins only because they shouldn't get us into hell. If driving two miles per hour over the limit increases accident rates by 0.000043%, and an increase in annual insurance rates of $0.00000079 per driver, then it's not really worth it to Caesar to pursue the matter. However, it is something we can choose to do or not to do. If it's not a morally neutral choice (and if Caesar is legitimately, reasonably, exercising his authority in proscribing one option, it isn't), and you actively choose wrong, you've got the elementary school textbook definition of sin on your hands.

It might not always be that simple, but it is that plain.