The context of the passage was the lie that Jesus cast out demons by powers of the devil. A better quote: "When a strong man like Satan is fully armed and guards his palace, his possessions are safe— until someone even stronger attacks and overpowers him, strips him of his weapons, and carries off his belongings." Luke 11:19-22 NLT
Figuratively, Jesus is the stronger power disarming the weaker so using this passage to support gun rights is improper. Don't twist scripture for political purposes like Wallis' ilk. Misusing firearms is bad, misusing Scripture is worse!
The 2nd amendment affirms the declaration that rights come from God & government is justified only by consent of the governed. See Exodus 22:2 for divine right of self defense.