Why do cops come to hostile situations with their guns drawn?

[KnighttimeJoe]

Because stuff like this happens.

Salisbury Man Randon D. Wilkerson Charged In Attacks Of Delmar Police Cpl. Keith Heacook, Elderly Couple

A Maryland man was in jail Monday on charges of attempted murder and assault in attacks that left a Delaware police officer with life-threatening head injuries and elderly couple with serious injuries.

news.yahoo.com