What I find disturbing about you question is its presumption that Christians want to kill unbelievers. Nothing could be further from the truth.
We Christians have been commanded by Jesus to take the gospel to all people. The mechanism for reaching unbelievers is *preaching* the good news that men do not have to die in their sins. Our weapons are spiritual not physical. Christ suffered death on the cross to atone for all sin. Forgiveness can be appropriated by receiving his sacrifice through the righteousness of faith. Men can avoid eternal torment and become joint heirs with the risen Christ.
It's hard to reach the lost with the good news, if we kill them. Every Christian was at one point an unbeliever. Many have heard the gospel, or various aspects of it, many times before coming to faith. Thank God that He is longsuffering and his followers are faithful in their perseverance.
I’m not the one who started quoting the Bible about God ordering the killing of witches. It was another poster who (I presume) is a Christian.