We're saying that checking the speedometer is a distraction from general awareness, while you're saying that general awareness is a distraction from general awareness.....
Nope. I'm saying that of all the things you need to watch out for, a lot of them will occur in front of you (pedestrians, sudden stops or slowdown due to traffic, animals in the roadway, etc). If glancing down at your speedometer is such a huge distraction, then logically speaking turning your head to the side to check your blind spots is an even bigger distraction. You don't need to worry about the dog in the road behind you because it's extremely unlikely to be a threat to your safety at that point.
And looking at the speedometer isn't even the reason I think speed limits are unsafe anyway. I've read a couple of those studies on areas where they do away with traffic laws and see an improvement in safety and traffic flow. The general observation is that people start paying more attention and communicating with each other, resulting in greater cooperation. Traffic laws cause people to default their behavior instead of compromising with the immediate situation. They assume that doing everything the signs & lights tell them + not speeding = the totality of safe driving, instead of actually paying attention to what the reality around them is doing.
I believe that's a fault of driver education, not road laws. Yes, I pay attention to the road signs, but I also assume that A: It's entirely possible to make a mistake, and B: Other drivers and pedestrians around me might not give a damn and act in an unsafe way. I see signs of children playing, or even if there are a lot of cars parked on the sidewalks, and I sure as hell slow down and give those blind areas as wide a berth as possible. I have probably saved at least one life that way.
Honestly, I think speed limits would be unnecessary if driving courses had a focused portion on breaking distance. That's really the only practical limit on speed.
That and the power of your engine. My 24-year-old car hates going anything above 80, despite the speedometer going up to 120. I'm not entirely sure it could even go that fast unless I was gunning it down a steep hill.
You should ideally be constantly scanning ahead for any obstacle that might enter the road in front of you, or any line of sight obstruction that could be hiding such an obstacle. If at any point you would be unable to break before hitting one of those obstacles, you're going too fast. If there's another vehicle in front of you, it's really simple. Maintain a safe breaking distance from that vehicle, and try to stay a couple steps ahead in identifying anything that might cause them to stop. Done.
This I agree with 100%. You should be driving at a safe speed for your current conditions, not going the speed limit (or over) at all times.
If you're on an open expanse of of three lane highway in good condition with no traffic around you on a flat landscape in broad daylight, there's really no practical reason you shouldn't be able to drive 100 mph if you want.
That's not really an option where I live, thanks to curving highways with lots of entrances, exits, and big rig trucks all over the place. I suppose it might work elsewhere, but around here going that fast is asking for either a ticket or a hospital visit.