Rants: WHY can't people drive at the speed limit -- no faster, no slower?

I've lived most of my life in cities & hence haven't spent a lot of my time driving, compared to most people. City rents & other expenses were so high that I walked, biked, or took public transit everywhere. Then we had a child who got motion-sickness on buses (NOT pretty) & for various other reasons decided to move out here.

So I finally bought myself an automobile. I quickly grew to love my car, because it's the quickest, most convenient, & safe-est mode of transport that I've ever known. Yet I also find it aggravating, because people are so danged self-centered & downright MEAN when they're driving. If they're in a hurry to go somewhere, they ride on your tailgate, honk, & flash their lights, even though I'm simply going at the posted speed limit ... um, okay, maybe 5-10 miles above the speed limit. I would gladly pull over & let them pass, but need to find a safe place in order to do so.

Meanwhile, other folks drive WAY slower than the speed limit & keep randomly STOPPING. Then they suddenly TURN left or right without flashing a signal. This also totally drives me nuts. Don't they understand that others need to get somewhere? Don't they know that they can turn around later if they miss their turn? Don't they know that someone might rear-end them -- or me -- if they keep driving like clueless slugs?

On the other hand, people drive through my residential neighborhood with narrow roads & no sidewalks, & children present, at high speeds because they think it's fun, & when you holler at them to slow down, they just speed up.

What the hell happens to people when they get behind the wheel of a car? Do they even know that anyone else exists? What drives me nuts is how common courtesy & basic civility seems to be suspended once a person gets behind the wheel.

What evolution of thought makes a person STOP thinking of a car as a three-ton, potentially lethal, & immense convenience & START thinking of a car as some sort of anonymous conveyance for their aggressions & hostilities?

Speed limits & traffic laws have been determined by people with graduate degrees in city planning & traffic studies from elite schools, who have studied reams & reams of data. Why do we consider our impulses & home-spun knowledge to be so infinitely superior that we are willing to risk unnecessary traffic accidents?