Radley Balko explains why SWAT team deployment has skyrocketed. A major factor:
The amount of force the government uses to uphold a given law is no longer determined only by the threat to public safety posed by the suspect. Now, it appears to give an indication of how serious the government is about the law being enforced.
The DEA sends SWAT teams barreling into the offices of doctors accused of over-prescribing painkillers not because the doctors pose any real threat of violence, but because prescription drug abuse is a hot issue right now. The feds sent SWAT teams into marijuana dispensaries not because medicinal pot merchants are inherently dangerous people, but because officials believe the dispensaries are openly defying federal law. It is, to put it bluntly, a terror tactic. Sending a couple cops with a clipboard to hand out fines and shut down a dispensary doesn't convey a strong message. Sending a bunch of cops dressed like soldiers to point guns at dispensary owners and their customers certainly does.
The Dish 