My vigilant observation has been that most people exceed the posted speed limits. The posted limits are NOT suggested speeds. They are NOT the minimum acceptable speeds. The number on the speed limit sign does not guarantee a minimum speed. You do not have a right to go at least the posted number on the sign. Yet most of us act as though that is exactly the information conveyed on speed limit signs.
NOT a suggestion
Of course it's "socially acceptable" to drive five miles an hour over the speed limit, to buzz cyclists and pedestrians and to talk (on cellphones) and text while driving. Ironically, while most motorists take these acts lightly, or at least not as seriously as they should, in most places there are specific laws limiting or prohibiting them. Unfortunately, laws that are broken that endanger, but do not explicitly harm, vulnerable users (of the roadways) are rarely enforced and the perpetrators get away with atrocious behavior until said behavior crosses the line and someone gets seriously hurt of killed.
The underlying problem is not the behavior, but the implicit approval of the behavior through our attitudes. If we were to demand better enforcement as a society, if we were to speak out against unruly motorists, even as fellow motorists, then we might eventually turn the tides and change perceptions.
My eight year old go onto me for yelling at a moving car from our lawn for going too fast on our street. He didn't think my efforts would be fruitful, but evidence supports that if a person is yelled at by enough of their neighbors they will begin to feel social pressure to change their behaviors. My verbal "SLOW DOWN" campaign may not do much initially, but I hope that it will catch on with people around me and eventually people will start taking back the roads from scofflaw motorists (and cyclists, I've started to yell at cyclists who blatantly break traffic laws) and begin reshaping our public perception of what is acceptable behavior behind the wheel.
And there are plenty of reasons to slow down while driving motor vehicles. You save money, the planet and your potential victims.
I'll leave you with this passage quoted in Zack Furness' One Less Car:
"Mass motoring effects an absolute triumph of bourgeois ideology on the level of everyday life. It gives and supports in everyone the illusion that each individual can seek his or her own benefit at the expense of everyone else. Take the cruel and aggressive selfishness of the driver who at any moment is figuratively killing the 'others,' who appear merely as physical obstacles to his or her own speed. This aggressive and competitive selfishness marks the arrival of the universally bourgeois behaviour, and has come into being since driving has become commonplace."
--André Gorz (pen name of Gerhard Hirsch, a social philosopher and political ecologist)