I am a Taco Bell-ian (though I have been known to stray)
Christians argue that an atheist, or other non-believer, is like someone in the street when a big truck baring down on them, a 'responsible' person would warn them of the danger. Thereby, it is christian's duty to tell the atheist of the danger of Hell, just as it is a bystander's duty to tell the guy about the truck.
What they don't get about this analogy is that the truck is real. Everyone can see the truck, the consequence of ignoring the truck is obvious, etc. Meanwhile, the christian truck is a magical invisible truck that is really nice even though it will kill you, and if you tell its your heart desire, it will give it to you... maybe. Meanwhile, 1000 other people are telling you about their magical invisible truck, bus, etc.