Police militarization has many causes and many bad effects. The pointless and faintly racist "drug war" is one that has been noted in many comments here. There's another that deserves mention, not because I believe it's most significant but because it seems strangely absent from those same comments.

>>> Police go in armed to the teeth in part because they believe (rightly or wrongly) that there's a high probability of the people inside being similarly armed. <<<

It's a classic arms race. Yes, the police should stop encouraging further escalation. So should others.