I think this quote from leonardo dicaprio sums up the reason they storm the house first and ask questions later. When leo is told that cops sometimes cry if they were forced to use their weapons, they have all those pretty toys, and nothing to do with them, you know they are just itching to try it out on someone regardless of whether the situation warrants it.
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"Use their weapons?
Let me tell you something.
They signed up to use their weapons.
Most of them, all right. But they watch enough TV...
...so they know they have to weep after they use their weapons.
There is no one more full of shit than a cop.
Except for a cop on TV."
Quote from AAAintheBeltway:
Let's say you( ie NSA) did stumble across a couple of suburban terrorist on long island. Would the clever thing to do be to send the local cops out to ask them if they had any bombs?
Or maybe would you watch them and see if they could connect you to someone else? Send out someone to do a blackbag job on their house when they were away?
These clowns are ridiculous. They spend tens of billions and can't keep track of two doofusses the russians ID'd for them. But they can roust you for googling the wrong thing.