People are evil. Not in the sense of "there are evil people out htere," but in the sense of "all of us are and do evil." We've all done things we regret, or should regret. We hurt or abuse or exploit others in our pursuit of self interest. We put our own convenience over the common good. This is just a part of human nature.
Liberals used to be the guys who said people were basically good and you should cut them some slack. Brian Covell has remaked that part of the decline of the American Liberal worldview had to do with our understanding of hte Holocaust as proof that human beings are fallen and sinful. The good pastor finds this somewhat lamentable, but after the events of the 20th Century, I would look upon with alarm any movement that claimed humand beings were perfect or perfectable.
Due to our sometimes miserable nature, life for much of human history was "nasty, brutish, and short." To deal with our insistant squabbling and murder of each other, the modern state evolved. Rules were developed for people to follow in order to bring relative peace to human relations. This was a vast improvement over the "warring tribes" system, which is what it replaced. In easter Europe, Somalia and Iraq we have witnessed what happens when the State collapses and we return to this brutish existance.
However, hte State has problems of its own. Basic human nature has not changed, so the people who run the government are also evil. They tend to use the power they have been granted to enrich themselves by exploiting everyone else, and work mostly to expand their own power.
To address this problem, Enlightenment thinkers such as the Founders of this nation developed a system under which the leaders of the government would be chosen by and held accountable to the people. Furthermore, they divided up the essential powers of the government among the 3 separate branches of government. They figured that the leaders of each branch woudl work hard to enhance thier own power. This would lead to conflict among the branches, often leaving them at loggerheads. While inefficient, this system would ensure that no one in government would be able to assert complete authority and misuse their offices too badly. The other branches would always be there to hold them accountable.
For example, the executive branch has the power to investigate criminal activity - this is an essential function of the state. Under the "warring tribes" system, when people wronged us, we would take our revenge upon them. In civilized society, we have given up our right of revenge to the State in exchange for its promise to protect us. So the State has a legal monopoly on the use of violence. They can grab people off the street, lock them up, and sometimes kill them. You, however, are not even allowed to throw a punch. "Assault," as it's now called, is a crime.
But what's to stop the leaders of the executive branch from using their monopoly on force to intimidate, threaten, blackmail and silence people in their own self interest? The answer lies in the separation of powers between the branches of government. The laws to be enforced are written by the legislative branch (Congress). Determining whether or not a law has been broken or properly carried out is the job of the courts. The executive just carries out and enforces the will of the other branches, it cannot make the law.
In order to protect people from tyranny, the system is set up to ensure that the government does not normally intrude on the privacy of ordinary citizens. Sometimes it must, but only to protect the public and enforce the law. But in order to do so, the executive must have permission from the other branches of government - they must present evidence to a judge that individual X has broken or is conspiring to break on of Congress' laws. This is part of the system by which each branch is supposed to be restrained by the other two.
So there's you philosophical primer for today. The real world relevance, of course, is that the Bush Administration now claims it has the right to invade peoples' privacy without presenting any evidence to the courts.
This amounts to saying "trust us. We're not going to use these powers against innocent people for our own gain becasue we're good people." But there arent' any good guys in real life, onlu uss self-interested pricks. It is necessary fro the government to investigate and detain people to protect the rest of us from the world of evil pricks outside the governmetn. But who protects us from the evil pricks inside the government? It's supposed to be the other branches of government. Public accountability through separation of powers and the rule of law. But by instituting large scale surveillance in secret, without informing Congress or the courts, the executive branch has proclaimed itself to be above the law.
"Trust us" they say. But trusting the people at the top to be nice is not a good plan for maintaining our liberty and ensuring that Americans will not be persicuted and jailed for political reasons. A much better plan is to keep the separation of powers and the rule of law in place.
We have maintained and expanded our freedom for over 200 years by not trusting anyone. We shouldn't let our fear of evil people out there make us forget that peopel are just as bad on this side of the border.