The people who are hired to "spy" on their fellow co-workers are generally looking for those types of violations and if somewhere in the middle someone is sending out porn, or using their employment at a prestigious company for ulterior motives, or any other myriad of the violations of common (or clearly stated at the time of your hire) corporate network use and they get caught, well... the flour sifter has caught a few more flies.
Despite the fact that we all work with them or are them, from the top tiers of management and from the shareholders viewpoint those violators are not the types of employees that you want to employ or want on the payroll.
Companies tent to benefit from firing these people because they show to their employees and clients that they are there to do business and just business.
If this was about ISP or the government spying on an individuals emails, then that would be a valid case and cause to rally the troops of the revolution, but when you are using someone elses network, someone elses resources, and being paid not to...well I don't really see the cause for concern.
Karl's version of Parkinson's Law: Work expands to exceed the time alloted it.