In a way, it's not too different from the kind of crazy logic that drives anti abortionists to murder doctors in the name of God who do abortions, or Islamic extremists to kill "infidels" in the name of Allah.
If you think God is on your side, telling you to do it, suddenly it becomes just dandy because God's commands supersede human laws or rules.
Let's all just be glad that the WTS doesn't wholeheartedly sanction outright violence, or some of the crazier Witnesses could get the idea that murdering worldly people was more productive than converting them.
According to their beliefs, it could be rationalized. Die now as a murder victim, get a resurrection as one of the "unrighteous" into the paradise. Die at Armageddon unconverted to Jehovah's Witnesses, you die forever.
You just have to get past that prohibition against murder in the Bible. Give them enough Bible hopscotch, could the JWs manage it? They got them to believe it's wrong to take blood and some other crazy stuff that way.
Although since the majority out preaching in some places are older sisters, the idea of arming them all with guns gets pretty silly.
"Watch out, JW Granny has a gun, and she's going to get you into the paradise the hard way if you don't read the Watchtower and convert!"