More directly, there are devices that have been shown to increase safety far better than speed cameras -- those electronic signs that ready your current speed back to you (and flash if it's too high).
Sure, a $100, $200, or more ticket is expensive and a lot of money to some people it allows the people who can afford it to easily rationalize the behavior.
"It's only $200 bucks it's clearly not that big of an issue, if it was a real danger it would be more expensive"
However the speed blinkers let you know you're doing something wrong and these condition you to feel guilty therefore slowing down.
I can honestly say that 90% of the time, I probably am not sure what the speed limit of a road is that I am on. I naturally slow down in residential areas, and speed up for highways. Generally this is 75mph or so in my area with a speed limit of 65mph. If they raised the speed limit to 85mph, I personally wouldn't really like it and probably wouldn't drive that speed.
I've gotten only one speeding ticket in my life, and I have never been in any accidents of any sort. The speeding ticket was on a 2-lane straight road, in the middle of the day with barely anyone around, so I was more comfortable with going fast and didn't even know I was going that fast.
edit: if you're going to down vote me, at least add to the discussion and prove me wrong.