ICP are essentially Evangelical Christian hip hoppers that are allowed to talk about bad stuff using bad words in a quasi-Marilyn-Manson-esque way.
Everything else goes hand in hand with any hip hop group -- delivery, talent, etc. -- that you'd see on the Trinity Broadcast Network... creationism, ignorance is bliss, and all that.
It makes their cult status and their being a target of humor less surprising, but still funny nonetheless.