The Bible doesn't support the idea of "let people do as they please to you for as long and as often as they like." And turning the other cheek was a response given to the hypothetical "if a man should strike you" and not "if a man should ram a sword toward your chest."
On the subject of violence, the Bible addresses anger, hatred, and revenge. All of these are destructive emotions/motives and can lead to making things worse. It is easy for people to confuse this with ALL violence including self-defense. Nowhere in the Bible does it say a man should abstain from defending his own life or that of others (especially his family).
There's an old joke about a man who hears that a flood is coming and refuses several offers for help claiming that "God will take care of me." In the end he drowns and, upon arriving at heaven demands to know why he was allowed to die. St. Peter replies "We sent you policemen, firemen, and a rescue helicopter... what more did you want?"
The point is that we are expected to do what we can, and rely on God to do what we cannot. Using a gun in self-defense is no less faithful than looking both ways before you cross the street.
Okay, I'm done with my soapbox... does anyone else need it before I put it away?