Because there is nothing more sinful than two people hugging with their genitals... ummm... face to face.
Look, I don't know what you fundagelicals are all on about with your purity ballz and your New Rebellion and your appropriation of hip-hop culture, but I'll give you one thing. This song is catchy. I mean, it cleared "MMM-Bop" right out of my head, so that's saying something. (Can I get a "hallelujah"? Okay, maybe not.)
Tim Foreman has a transcript here. Which provides more questions than answers. Like, what's the difference between a Christian side hug and, say, a Shinto side hug? What is inherently sinful about the front hug, other than two people's crotches lining up? What if one person is a lot shorter than the other? Can they "front hug" then? If it's okay to "front hug" after marriage, is it okay if two married men "front hug"? Or is that totally gay?
And why the fuck is everything all about sex with you?
See also Feministe and Feministing and just about everyone else on the internet.
[H/T to my pal Lena, who side hugs like a motherfucker.]