Mum's in a high rise just beside a busy road. When visiting her, I often stand at the kitchen window and watch the various vehicles go by. The amount of speeding and tailgating witnessed is always on the high side. Comes back to what I said before, how dare anyone drive on or near the speed limit.
As for this theory of it's ok to drive faster if you've accurately judged the road conditions, where do you draw the line with such a theory? Let's say there's a 30 limit stretch of road in a built up area. You enter the area, assess the road and surroundings and determine in your opinion it's safe to drive at 40-45, maybe even 50. After all, you're a competent driver, so what's the issue?
You're driving along then, out of nowhere, a pedestrian runs into the road. Maybe the old cliche of a child going after a football they were safely playing with in their garden.
BANG. You hit them, cause you couldn't stop quickly enough. They're dead. You've killed them.
If that happened to you, I suggest you'd be wishing you'd adhered to the speed limit for that stretch of road, or at least stayed within 5mph of it.