RE: daytime lighting is a good thing. When it's bright you'll see the lights before you see the vehicle due to glare or harsh shadows. In winter when everything is gray and dull and cars are covered in salt, sand, and snow it really helps them to stand out from the background.
RE: speed limits, if you read the actual laws in your states typically have four parts. One, allowing for localities to set speeds lower than the state max on everything other than interstates. Two, that speed is dependant on the conditions. Three, minimum allowable speeds on certain roads (25 is the min in Vermont). And, four, what fines may be levied.
Max limits are set using a variety of design metrics. One being the safest distance you can reasonably see around line of sight obstructions. If the limit is 40 and you use one second for every ten miles per hour then you should be able to safely see up the road four seconds.
That being said The Eisenhower Interstate System was developed to consistently handle about 70 mph at a time when cars were generally unsafe at those speeds for an extended period of time given tire technology and so on. I don't think it unreasonable to be able to do 80 or more on some stretches of Interstate in this day and age.
I teach DE in Vermont. I am astounded by many of my colleagues inability to grasp the nature of vehicle dynamics at speed. We don't teach it either. Our model is based off a model leftover from the 60s. Not a good one either. We are about 42 or 43 in the industrialized world for fewest motor vehicle fatalities. At one time (the 80s) we were at or near the top. Both England and Germany (two countries analagous to ours where driving is concerned) are now in the top 3. What changed? Their politicians decided to risk it and require true driver training. We did nothing. The manufacturers don't want to wait an additional year or two to sell cars, parents are pushing to have kids driving as soon as possible to alleviate the parent taxi syndrome, and legislators fear the backlash from strengthening the requirements and the testing because it might cost more. We, on a state by state basis, severely curtailed or eliminated DE over the last thirty years. Only about 14 states have any semblance of a DE program that is mandatory. And some of the ones that do merely require passing an online class with no seat time with an instructor.
So what does all this mean to the OP? 80 in a 70 is not unreasonable under the right circumstances. But, until we look in the mirror and blame ourselves for neutering driver education for fear of higher costs, convenience, or loss of sales the arguments will continue. Better DE that has at its core more actual driving time with trained instructors, over a longer period of time, and licensing at a later age will go a long way towards solving many of the issues the safety advocates and the enthusiasts have about driving in this country.
Want to know more? Check out Andy Pilgrim's Traffic Safety Education Foundation.