It's about fatalities and serious accidents... The number of accidents from things like "lane hogging" (where things like road rage comes in), driving while talking, and headlights... PALE in comparison to accidents caused by a speeding motorist. Their job is to PROTECT the people, that protection is significantly improved when speed laws are enforced.
If cops were trying to be dicks and just ticket people for speeding, everyone going 1-4 MPH over the speed limit would be ticketed, and everyone knows that is not the case.
I regularly pass police going 5-7 mph over the speed limit and the officer wont even blink. I have been TOLD by many officers and hwy patrol as long as I keep it under XX, I will be fine. One of these being a highland heights officer on i75 (they patrol the shit out of that stretch of 75), that as long as I kept it under 70mph (the speed limit is 55mph there) no one would ever bother me. (he even let me off with a warning that night). And guess what, I have proven that point many times.
In general, police will NEVER have a good reputation when it comes to traffic law, because 90% of people will complain when they get a traffic ticket. And the excuse is usually always hte same "why dont you after real criminals" guess what? they do that was well.
PS, I say that as someone who has had their licence revoked for pts (13 pts) all due to speeding, and has been pulled over more times than I have fingers and toes. And while it sucks every time I get a ticket, I STILL respect the officers position.