Well, there were people defending the idea of Earth being flat until their webpage got hacked, not long ago.
And as for your example, yes. If the confrontation with that person escalated into a situation in which my life was in danger, I wouldn't hesitate to use lethal force. But that's just me.
How so? Obviously a nuclear blast will have more power to spread the nuclear waste, but as far as I know, radiation from the blast itself is pretty short-lived, albeit quite lethal.