"They're so happy-go-lucky, kind of optimistic people, and they kind of have that cheesy factor," Parker said. "It's like Mormons, Disney, Rogers and Hammerstein, it all kind of makes sense...Mormons are just happy people so you're going to get a happy musical out of it."
After over a decade of amusing and offending America with their smash-hit cartoon, "South Park," on Comedy Central, the duo took a leap of faith into their Broadway debut with "The Book of Mormon," which has already earned them critical acclaim.
The musical, which opened Thursday night at the Eugene O'Neill Theatre in New York City, tells the story of two Mormon missionaries in Uganda.
Although it was written to poke fun at the Church of Jesus Christ of Latter-day Saints, Stone reiterated that the "Book of Mormon" was not meant to just mock Mormonism, but religion in general, calling his show, "an atheist's love letter to religion."
"Anybody's religion, to an outsider, it's just as goofy," he said. "I don't think either of us think Mormonism is any goofy-ier than Hinduism or Christianity, from an outsider's point of view."
But taking on religion in a comedic way with "The Book of Mormon" was entirely different for the duo.
"None of us ever sat down and said, 'OK, let's go after Mormons! Let's get them! And how can we do that? Let's do a Broadway show,'" Parker said. "I love the format. I love the oldies. I love the classics. I love 'Oklahoma' and 'South Pacific' and mostly the Rogers and Hammerstein musicals."
"We grew up in Colorado," Stone added. "So Mormonism and Mormons, other than Utah, is right next door, so there's just a lot of crossover there, and we both knew a lot of Mormons growing up and it's always fascinated us."
A project that has been seven years in the making, the show's plotline changed dramatically since the two first came up with the idea. Parker said they originally wanted to write a story about Joseph Smith, the founder and prophet of the Mormon religion, but that a "covered wagons musical" wasn't going to work.
Trey Parker and Matt Stone on Writing Musicals
"We realized that most people's interaction, first interaction with it, is with missionaries," he said. "Those guys in the white shirts and ties that ride around on bicycles and go door-to-door."
Both men said they are big fans of musical theater, and have often written show tunes for the crude cartoon characters of "South Park," some of which have mocked religion. One example is the popular ballad sung by the character Kyle, "It's Hard to Be a Jew at Christmas." The 1999 "South Park" movie, "South Park: Bigger, Longer, Uncut," showcased a song, "Blame Canada," that was even nominated for an Academy Award.
"We just cover an enormous amount of ground that you couldn't cover if we didn't do it through song," Stone said of doing "The Book of Mormon."
The Creators of 'South Park' on Fatherhood
Despite both men now having children in their lives, fatherhood hasn't seemed to slow down to soften the kings of vulgar cartoon comedy.
"I think there are people who are 30 who shouldn't watch 'South Park'," Stone said, laughing. "I have some friends who shouldn't be watching it. I always thought 'South Park' for about [age] 12...that seems about right."
Parker said that while he lets his 10-year-old stepson watch some episodes of "South Park" with him at home, there were times that he felt compelled to cover the young boy's ears during "The Book of Mormon."
"There's some hard-core stuff in the show, but it's not worse than a lot of 'South Park' episodes," he said. "We're able to pretty much say when people ask, 'oh can I take my kids to see this,' we're like, 'do you let your kids watch any episode of 'South Park'? If they say, yeah, we say, yeah, bring them."
The statement to ABC News from the Church of Jesus Christ of Latter-Day Saints said: "The production may attempt to entertain audiences for an evening but The Book of Mormon is a volume of scripture that will change people's lives forever by bringing them closer to Christ."
Parker jokingly boasted that he would give free tickets to members of the Mormon faith, including potential presidential candidates such as former Massachusetts Gov. Mitt Romney.
"We don't want to go out and make a Broadway show that's cynical," Parker said. "The thing I love about musicals is sort of how happy and optimistic a lot of them are...that's how a lot of them made me feel."