As Balko wrote in the executive summary to a white paper for the CATO Institute on the subject in 2006:
These increasingly frequent raids, 40,000 per year by one estimate, are needlessly subjecting nonviolent drug offenders, bystanders, and wrongly targeted civilians to the terror of having their homes invaded while they're sleeping, usually by teams of heavily armed paramilitary units dressed not as police officers but as soldiers. These raids bring unnecessary violence and provocation to nonviolent drug offenders, many of whom were guilty of only misdemeanors. The raids terrorize innocents when police mistakenly target the wrong residence. And they have resulted in dozens of needless deaths and injuries, not only of drug offenders, but also of police officers, children, bystanders, and innocent suspects.One of the key recommendations in that CATO white paper was to "Return SWAT Policing to Its Original Function—defusing those rare, emergency situations in which a suspect presents an immediate threat to someone’s life or safety. SWAT teams should not be executing search or arrest warrants, conducting routine police patrols, or engaging in similarly proactive police work. SWAT teams should never be used to serve search warrants on drug offenders with no history of violence." I couldn't agree more.
SWAT teams were originally inspired after the Charles Whitman UT-Tower shootings here in Austin, but increasingly they're used for execution of routine arrest warrants instead of intervening in already violent situations, initiating violence instead of quelling it. Here's an interview with Mr. Balko from earlier this year lamenting the unnecessary trend toward SWAT teams' overuse.