Erm.. I don't know what speed limits are like where you live but here you would fail your driving test for using an inappropriately slow speed on a dual carriageway (here the limit is 70). The only time I subscribe to the whole speed kills stuff is around built up areas, where accidents are often out of the drivers hands and simply hitting a pedestrian slower may make the difference. Apart from that driving round a built up area making lots of noise is disrespectful and makes you look like a muppet.
The vast majority of the time though the speed limit has nothing to do with what is a safe and sensible speed because if you were actually to set a sensible speed limit for a road it would change every 10 yards and still couldn't perceive danger, it's why a computer will never be able to safely drive a car in the real world. Choosing to drive quickly on a road you know isn't necessarily more dangerous than driving down it slowly, if you drive quickly but still well within your limit you'll be far more likely to realise a problem and be able to do something about it before it's too late, in reality modern cars do stop very quickly from fast road speeds if you react soon enough and can keep them on the black stuff. Someone whose driving down a road at the prescribed speed limit and half asleep simply will not recognise the danger as quickly and in the end of the day pile into what ever it is faster than the guy who can react in time, the vast majority of motorway pile ups are caused by people who are either half awake or using stupidly excessive speed for the conditions, doing 70 on a packed motorway through standing water is suicidal but you see it pretty much everytime you drive in those conditions but you see idiots doing it still because it's the speed limit. One of the worst road accidents I've seen was a Metro that was doing about 50 in the slow lane that we passed, then 30 seconds later the motorway ground to a halt (there had been no shortage of warning signs), he just drove straight into a row of stationary cars, obviously the speed of the impact is what led to him being dragged out his burning car but it wasn't his initial speed that had anything to do with it.
The closest call I've had was with a Lancia Fulvia that had obviously gone far too fast into a corner at about 20mph (in a 60 limit) having failed to read the fact there was about an inch of standing water on the road, thankfully he was going up a step gradient at the same time so gravity stopped him, with a large drop on one side of the road and a rock face on the other side there was nothing I could do but try and stop, luckily I had already seen the water ahead and worked out that I didn't fancy going round a blind downhill bend full of standing water in a hurry and had already slowed to walking pace so could stop in time. If we had hit head on at low speed and both ended up down the drop it wouldn't suprise me if it was a double fatality from excessive speed at a fraction of the speed limit, in contrast one can drive down a straight desert road with good visibility at 150mph perfectly safely, of course an accident would be far worse and you take the risk of a mechanical failure but in the end of the day you're far less likely to have a crash than you would on a wet narrow twisty road at a bit above walking pace that can in the end of the day still result in multiple fatalities.
Like Tristan said driving a car is by far the most dangerous thing any of us will ever do, I bet if you worked it out motor racing is far less dangerous than driving in the road. Hitting something is bad however slowly you hit it and when you have high speed multiple car accidents the results can be horrendous, one of the worst scenes I've seen has to be body parts lying in the middle of the carriageway, I'm fairly certain that one wasn't caused by a car doing excessive speed either, of course some are and it's a risk we have to be a prepared to take if you want to drive fast, what's important is you understand the risk and don't put others who haven't chosen to take that risk into jeopardy.
And I agree with the rest of your post too 
they leave it too late before deciding to overtake and then only speed up a little from a standing start rather than anticipating an overtaking oppertunity.
illepall