Enforcement of the law is a funny thing; too little, and anarchy reigns, too much, and you're in a police state. I'd posit that neither of these extremes are desirable, and that a nice happy middle ground is a good place to be. Such a middle ground requires a balance of power though, and in the US that balance is perceptibly shifting in favor of the state.
Three reasons come to mind that are allowing this shift to take place and take hold. First, advances in information technology enable the collection and processing of data in ways that are orders of magnitude more efficient than even just a decade ago. Second, the development of a fear-based security apparatus in the wake of multiple terrorist attacks in 2001 has lessened the traditional emphasis on citizen's civil rights. And finally, the successful anti-tax campaign of a host of political demagogues has brought about systemic dysfunction in the way we finance government operations. Add in the delightful bonus of a crippling financial crisis, and you get a political environment tailor-made to strip power from the citizenry.
One of the more prevalent but perhaps less obvious power shifts has been occurring in the world of traffic and parking enforcement. Until recently these functions were performed by paid, often sworn officers of the city and state. Their numbers were constrained by budgets, and their enforcement efficiency (simplistically, # of tickets per work hour) was largely constrained by limits of human ability. Also notable is that the issuing authority was a human being, with inherent (though variable) capacities for judgement and reason. Under this system there were multiple levels of appeal for an infraction, starting with the issuing officer, and moving on into the courts. The issuing officer was also able to take other factors into consideration, such as: was a good faith effort made to obey the law? were there extenuating circumstances that led to the violation? did the infraction fall into a modest "grace period"? And in many cases the officer had the ability to proffer official warnings that were intended to influence behavior without requiring penalty payment.
The application of advances in digital imagery, networking, and data processing are upending the traditional détente between motorists and government when it comes to traffic enforcement. In areas of speeding, parking, red-light running, licensing, and registration, automation has been brought to bear. In many communities this was done explicitly as a means to generate additional revenue for the government to perform operations. Here in Chicago, the Department of Revenue patrols city streets with camera vans in search of scofflaws parked in their own neighborhoods. Thanks to their diligence I have received tickets for a "missing" city sticker (obscured by snow on my windshield), no front plate mounted (it fell off after being backed into, and as it was too cold and rainy for it's sick owner to reinstall promptly, I had placed it visibly in the front windshield), and no front plate mounted, again, three days later (I was still sick). If I had left the car unattended for a week without reattaching the plate, I probably would have received my third ticket and perhaps a boot, to boot...
In addition, Chicago has plenty of company in the deployment of red-light cameras throughout it's lands. Roll-outs of these devices are often couched in terms of public safety, but there is significantly conflicting evidence regarding before-and-after accident rates. Instead, these devices are often installed by privately owned firms that receive a cut of revenue generated by their cameras. Initial review of potential violations is performed by the same private firm, and those instances found most likely to generate revenue are forwarded on to a government official to authorize issuance of a ticket.
Concerning privacy, the city of Chicago continues to claim "Red-light cameras only capture motorists who have broken the law" . This is demonstrably false, as the video segments provided to offenders show several seconds of intersection traffic while the light is yellow. As for slippery slopes, members of Chicago's City Council have also considered using the cameras to enforce mandatory auto insurance requirements as another revenue-generating privacy invasion. And in California, Gov. Schwarzenegger is proposing the use of speed sensors in conjunction with cameras already in existence to help plug massive holes in the state's budget.
These systems have their place, but the motivating factor for law enforcement should not be revenue generation, and that's where these run off the rails. Law enforcement should have the public safety as their primary goal, and government should primarily operate within the budgetary constraints provided by taxation. Anything else is a distortion that needs to be addressed.