But why do:
People occasionally speed past a police car on purpose.
Do you actually know a single person who dutifully obeys the speed limit until he sees a cop, at which point he guns it so as to be sure the cop sees him speeding? Yeah, I didn't think so. Now, I have occasionally been running a few miles over the limit, and therefore technically speeding, and not slowed down when I saw a cop, but only because I was reasonably sure he wouldn't come after me for doing 5 over when there would be someone doing 15 over coming along soon. It takes the same amount of time to write a 5 over ticket as a 15 over ticket, so the vast majority of cops will ignore 5 over to maximize revenue by only going after 15+ over. Do you think god usually ignores the adulterers and graven image makers but always drops the hammer on the murderers and baby rapers? If not, then you've made a false analogy.
They drink and drive, knowing the consequences.
No, they drink and drive knowing the potential
consequences. There is always the possibility they will make it home without being pulled over or causing an accident. Again, unless you believe in a god that is either not omniscient or or does not persecute all sin consistently, this is another false analogy.
They know the speed limit is 65, yet they go 66.
I think we already covered this one above.
They know killing is wrong.....not for God, but for THEM....yet they do it anyway.
Everything points to a state where we know better, but break even our own rules anyway.
The reason people break the laws of the land is because they think they can do so without either getting caught or getting punished, which would not be possible in the case of an all-knowing god. So you've not answered the question. Why would someone who truly believes god is omniscient ever sin?