I disagree. You should, as a competent driver, always be aware of your speed. That does not require staring at the speedo - the information is quickly and easily gained in a passing glance, combined with your own experience and judgement. Speeding fines are voluntary payments.
Hard to tell what you disagree with, as I made several points.
However, I disagree with your single point. It is impossible to stick to the exact speed limit. Road contour, speedo errors/jitter, wind conditions etc can all contribute to a slight variation in speed.
Even the most competent driver in the world could not drive the limit.
If police do not want drivers to exceed 50kph in a 50 at all, it would be preferable to reduce the speedlimit to 45kph with a 5kph tolerance. Many of our open roads are completely unsuited to a 100kph speed too. In those cases i'd support 0 tolerance, or, even better a reduction in the actual limit.
So err on the safe side and drive at 5kmh less than the speed limit. I have been driving for over 30 years and have less than half a dozen speeding tickets in that time, every one of which I fully accept was my fault for not paying attention.
It does not matter what the limit is: it is not a target...! It is the driver's responsibility to decide what speed is correct up to that maximum. Take for example a random 100kmh road: if the limit was raised to 500kmh, you would have to be stark staring mad to even consider driving the average NZ road at that speed despite the fact that legally you could.
I absolutely agree that the limits are wrong in many cases, simply because there are many idiots on the road who are unable to exercise judgement when deciding what speed is appropriate and they are in need of being told to only drive at 80 or whatever instead of 100. They will probably still speed, because they are bad drivers who think rules apply to anyone but them, but you can't legislate for idiots in advance really. I suppose we could set a minimum IQ of 120 for getting a driving licence but I suspect that we would be short of a lot of necessary drivers if we did...!