Ive lived in a lot of different states over the years. Surprisingly (to me at least), the seeming sensibility of speed limits seems to vary quite a bit depending on the state you are in. Midwestern states seem to be more conservative, while western states seem to be less so. Southern states seem to be hit or miss. Either way, I think its a bit naive to suggest speed limits are only for revenue generation, or strictly based on safety. The truth lies somewhere in between.
You saying the OP was traveling on a road that could easily support 45mph is simply a guess on your part. Yes speed limits tend to be rated conservatively more than recklessly (obviously), if in either direction... but some speed limits are right on the money. And speed limits have to take all situations into account.. is it a bright sunny summer day with high visibility, a foggy fall evening when visibility is poor? Is it raining heavily? Snowing? All these situations have to be accounted for, and leaving that up to each individual driver would lead to abuse based on the notion everyone thinks they are an above average driver, or above the rules. And sometimes statistics point out problem areas that common sense does not detect. Who knows why some certain seemingly innocuous curve on a road claims a statistically high number of lives each year, but if it does, it is the govt's responsibility to address the problem.
In the end, I guess I'll be that do gooder you talked about and say obey the speed limit. If the speed limits in your area are unjustly low, we have a system in which you can voice your opinion. Plenty of ways to do so. If you chose not to, and simply break the law... fine. But dont come here and ***** you were treated unfairly when the cop didnt let you off with a warning. The way i see it, you dont just take your life in your hands when you speed, you take the lives of everyone around in your hands too. A responsibility many people take far too lightly these days. Do I speed sometimes? Sure, im not suggesting I dont. But Im not so naive as to suggest there is no good reason for speed limits other than to generate revenue, or suggest most all speed limits are too low. But then, Im not so important that my time is too valuable to not be worth allowing me to leave for my destination 1-5 minutes sooner so that I can get there on time without doing 9mph over the limit.
If you want to discuss revenue, lets look at the other side of the coin. Its well know cops let people go 5mph over the limit before even considering pulling them over (usually). In my highschool drivers ed class years ago, the officer who came in to talk to us even said this. What happens when the vast majority of people assume they have the right to break the law by 5mph? The cops then have the right to pull over virtually anyone, at any time. Bam, automatic insurance policy to generate revenue, and to invade our privacy virtually at will. But as said above, if you want to fight this, dont use that 5mph that they 'give' you. 9mph? You should assume you'll get pulled over for that if a cop sees you. And assuming you will get a warning is just being naive. Complaining about it here only shows a lack of experience in dealing with this situation.