Prevent terrorists from killing Christians, enact that LAW !
You and what army?
You can storm like that until doomsday and what is it? Proud posturing, proud in the arm of flesh that thinks it can open selective spigots of heaven rather than accepting the river of God’s grace ready to be had by those who will acknowledge it.
I.e. if Christians themselves, who are of all people most in a position to know, won’t embrace and cherish in their heart the full love and counsel of God in the very Person of Jesus Christ (not some selective thing like you have touted over and over)... they should not EXPECT any help from heaven. They’ve opted to be in a region of hell. They will reap its rewards. Even ATTEMPTS to enact such a law will be rebuked so thoroughly that it will result in lasting difficulties (USSC precedents, ever hear of them?) even in a new age of grace. Because those who did so thought they could, in their filthy wallowing sins, merit it.
If there IS to be a mutual protection regime it won’t happen by law, even though that is the only force you seem to know. It will happen by grace, by the voluntarism of willing hearts that discover God’s true Love.