Just checked the stats with our researchers where I work.
Lorries = 51 accidents per hundred million vehicle kilometres
Cars = 94 accidents per hundred million vehicle kilometetres
Anyway, I admit we've strayed from the point here, and I didn't mean to make this personal, so sorry if that's how I've come across.
Most folks who've contributed have agreed that bad driving causes accidents, and some of that bad driving is driving too fast.
I agree that most people on the motorways seem to do nearer 80 rather than 70, and most of the time that seems fine and dandy. But, we all see people travelling at nearer 100, and bullying people out of the way by tailgating, and undertaking if you dare stay where you are.
My point, if there is one, is that whether the limit is 70 or 80, there is very little to be gained by exceeding it by a great deal, except stress, higher fuel consumption, antagonising your fellow road users and ultimately the risk of losing your licence. Where has all the courtesy gone in driving today? And, I suppose, the fact that even 10mph slower could mean the difference between life and death if you got involved in an accident, either your own or somebody elses.
I respect that you have a different view about some of that, but speed enforcement is, I think, a legitimate and necessary thing given the situation we find ourselves in roads wise, as people seem incapable of driving responsibly, or even sticking to the most sensible speed limits, especially in built up areas, without some kind of penalty system hanging over them.
By way of example, walking down my village main street, which is an A road, was a terrifying experience before speed cameras were put up, and the difference is amazing. Not that there were many fatalities before mind, just that now everybody feels safer.