It's Unconstitutional: The Constitution is largely a document of limits- limits on the ways in which Government may interfere with our lives. The Bill of Rights (the first ten Amendments to the Constitution) is a short list of specific aspects of our lives which Government may not interfere. The 4th Amendment clearly prohibits such sweeping invasions of privacy and property as Carnivore commits.
It Threatens Freedom and The Internet: The best thing about the Internet, the thing which has allowed it to prosper as much as it has, is lack of centralized control. An while there are those who would use this lack of control to their criminal advantage, it would be a far worse consequence to give up the "chaos" in favor of stringent control.
All of the wondrous possibilities that the Internet offers us come at the price of it having no central control or governing body. To impose that type of control will be at the expense of the freedoms which have made the Internet what it is today. For 30 years, Government control stifled and suppressed the growth of the Internet. We must not allow such a fate to be reinstated.
It Sets a Bad Precedent: What if the FBI said they wanted to monitor all telephone calls, for information about suspected criminals? What if they wanted to intercept all postal mail, to check and see if any of it was related to any of their suspects? What if they wanted to do a "profile" of the average marijuana user, by scanning huge amounts of electronic data, and compiling the marijuana-related communications? What if they wanted keys to everyone's houses, in case they had to get inside to investigate a crime? Use of the Carnivore system plants the seeds for all of those types of developments, and many more frightening ones.
It Will Harm Innocent People: The FBI can hardly be trusted to conduct their investigations with proper handling and precision, but even if they could, Carnivore will end up hurting innocent people. The amount of guesswork involved in a sweeping search like the type Carnivore does insures that many "dead ends" and "bad leads" will be pursued. What this means is that the FBI will inevitably end up investigating (including search, seizure, intimidation, prosecution, etc.) innocent people. The use of a mass-level tool like Carnivore simply insures that these will occur more frequently, and at a more widespread level. (