Jan. 30, 2007  -- Brian "Sapient" is an average-looking 30-year-old guy who works out of his basement in Philadelphia. His job? Well, Brian is taking on God.

"Wow, that's a dramatic way of putting it," says Brian, who asked that "Nightline" not use his real last name for safety reasons. But however he defines his challenge, Brian is on the cutting edge of a new and emboldened wave of atheism.

"There isn't any good reason to believe in God," asserts Brian. "It's that simple."

What's wrong with God?

"What's wrong with the tooth fairy?" asks Brian. "There's nothing wrong with something that most likely doesn't exist."

There are an estimated 20 to 30 million atheists in the United States these days, and some of them say they feel like a persecuted minority.

"Atheists are completely vilified. And it's OK," says Kelly, an atheist who works alongside Brian and also asked that her last name not be used.

"It's actually OK to hate atheists," Kelly said. "We are like the last group that people overwhelmingly agree that it's OK to hate us, because there's an absurd caricature of atheism out there."

The Rational Response Squad

Brian and Kelly are co-founders of the Rational Response Squad. From Brian's basement they broadcast a weekly Internet radio show about God or the lack thereof.

And recently they came up with a new way to publicize their cause. It is called the Blasphemy Challenge.

"Initially we wanted to find a way to allow atheists to come out of the closet, speak up and show other people that there are people that think like this," Brian says.

What they did was challenge people to make videos of themselves, denying, denouncing or blaspheming the Holy Spirit, and then post them on YouTube.

'We Are Not Scared of This Unforgiveable Sin'

"We wanted to do it in such a way where we stripped the power from religious institutions that instill fear in people," says Brian. "And we did that by blaspheming the Holy Spirit, by showing that we are not scared of this unforgiveable sin."

A passage in Mark 3:29 reads, "whoever blasphemes against the Holy Spirit will never be forgiven; he is guilty of an eternal sin."

While the passage is open to interpretation, the Rational Response Squad is taking it literally and challenging people to gamble with their eternal souls. So far more than 800 people have taken up the challenge.

One of the posts is by a young-looking man named Chandler. He says: "I've come to the conclusion that alongside the fact that there is no Santa Clause and there is no Easter bunny, there is also no God. So, without further ado, my name is Chandler and I deny the existence of the Holy Spirit."

Another: "My name is Joel. I deny the Holy Spirit, as well as God, Jesus, Buddha, Zeus, Mohammad, Joseph Smith, Sponge Bob, the pope, Santa Clause, Mother Mary, the Easter bunny, the tooth fairy, Optimus Prime, all the saints and Spiderman."

Dozens upon dozens have posted, including comedian Penn Jillette, who simply says, "I deny the Holy Spirit."

'Eternal Trouble'?

"I think how sad it is that someone would be rejecting hope essentially," says the Reverend Kathleen Liles, an Episcopalian minister, just one of many from the religious community who say this Internet challenge is misguided or worse.

"I think if people are courting blasphemy, going out of their way to cross that line, that is just dangerous," says Paul de Vries, the president of the nondenominational New York Divinity School, which provides ministry training. "They might get themselves in eternal trouble."

Brian thinks otherwise. "We are showing people that we are not afraid of what they are afraid of. He is saying that he is afraid in that situation. He is saying how he would feel if he were doing it himself. He would be afraid. I am not."

Targeting Teens

Taking risks with your own soul is one thing, but the Rational Response Squad advertises for the Blasphemy Challenge on Web sites for teens, like Tiger Beat. Why?

"They have already been targeted," Brian says. "So hopefully they are at a point where they are not so indoctrinated and set in their ways that they can overcome this religious superstition that has been put into their brain unfairly."

Isn't that simply another attempt at indoctrination?

Brian says it isn't.

"We are not indoctrinating people," he says. "There is no fear of hell in what we do, in our activities. We don't tell people that if they do believe in God they are going to hell. We are against fear-based systems."

Brian wasn't always an atheist. He was raised Catholic, and became a born-again Christian when he was 13.

"That's what I was taught. And I really believed," Brian says. "I loved Jesus and he was my best friend and I talked to him and God all the time. I have to admit that they never talked back to me, and I think some people would say that God does talk to them and I think they're not being honest with themselves."

'The Faith to Believe'

Liles says Brian is simply missing the point. Faith is not something that can or should be proven, she says.

"Faith is a gift, it is a mystery, as so many other gifts from God are," she says. "And when we open our hearts to God, then God will give us the faith to believe."

However Liles feels about atheism, it isn't going away and might even be getting stronger. Two of the best-selling books on Publishers Weekly's religion list are by atheists about atheism. There is a hard-hitting documentary questioning the very existence of Jesus. There is even an atheists' lobby in Washington.

Brian's decidedly black-and-white rhetoric has won him many enemies. He has received hundreds of death threats from Christians using decidedly un-Christian language -- more four-letter words strung together in a row than you can imagine.

Like his last name, he keeps his address a secret for safety reasons.

Despite the threats, the Rational Response Squad intends to keep Blasphemy Challenge going for some time. "Until the end of Christianity," Brian says.

Do Brian or Kelly worry their rhetoric and antics might land them in hell?

"No, because hell doesn't exist," Kelly says.

Even if there was a one in a million shot that Hell existed, would they still be so unconcerned?

Brian's response? "That would stink, huh?"

The jokes about hell and the whole Blasphemy Challenge open the squad up to critics' attacks who say that whatever its views, its methods are simply disrespectful.

"If I knew that their belief system was wrong and I didn't say something, that would be much more disrespectful," Brian responds.

And to the billions of Christians who have believed for the last 2,000 years, Brian says he is open to a dialogue.

"If they want to come to the table and present their evidence, I will present my evidence. And we will see how much of theirs is based on faith, and how much of mine is based on fact."