Turning the other cheek relates to individuals, not to the whole country. We could very easily have a large portion of our country newked if we aren't prepared. While I am a hypocrite, as I am as quick as anyone to knuckle up, I do agree that the Bible as individuals calls us to love our enemy, but I can show you numerous examples from the Bible where God gave his people the strength to win battles and wars.
I know I have approached this strictly from a christian worldview, but that's where my values come from. From a secular worldview, my job takes me into some high crime areas at times and I am going to get home and see my son each evening. I am going to protect myself because I understand that evil people exist and will always exist. It works the same way with our leaders protecting the country.