Recently, as a part of Halloween, I learned about an interesting building known as a Hell House. Apparently, some Christians decided they didn't like Halloween and instead put up their own haunted house tour that involved a ton of different sins, what you have to do to be absolved of them, and what happens if you don't do those things. They find these things to be terrifying and a real wake up call, much better than any Halloween activity. In fact, this kind of attraction has spread all over the US, especially in the heavily Christian areas. So it comes as no surprise to find this question being asked every year.
"Why aren't Atheists affected by or concerned with what they see in a Hell House?"
Well, the answer is quite simple. We've seen worse. In Haunted Houses, in Halloween movies, in chilling video games, we've seen far worse things done to far more innocent people. Sure, the real thing would still churn our stomaches, but more fakery will do nothing.
However, I don't think that's what the question is really asking. I think it's asking on a spiritual level. Well, that's a little harder to explain without offending anyone. I'll do my best, but keep in mind that I have no intention of offending anyone at any time.
Basically, we don't see any of it as real or anything to worry about. That should be no surprise by now, but for some reason it still is. Atheists typically don't believe in souls or an afterlife or any kind of deity that will punish us. And the typical Hell House is chock full of misrepresentations. For example, Magic the Gather leading children to "the occult" is a flat out lie. If anything, it keeps them away from it as it shows them that, should it really exist, magic can be very dangerous. And, besides that, it's just a card game. It's not like they actually think they are casting creatures to do their bidding. Also, the "occult" is not always bad, either. There are those who practice only white magic, abilities meant to only help others.
With all of the inaccuracies and corny acting, the typical Atheist will have a great deal of trouble keeping from laughing, even if they are a very nice person, willing to hear out the host's views. This is why they are ineffective. They have a great deal of misinformation and they don't target the things Atheists typically care about. These houses are usually geared toward preaching to the converted and their children, keeping the new generation grounded within the confines of their religion.
You can't expect that kind of thing to win over a steadfast disbeliever, now can you?