If the transcript in the blog post is accurate, I fail to see why people are getting so offended. He didn't call her names, he didn't directly insult her intelligence, he just highlighted her speech impediment. Should I be offended and mobilise the klan if I call up and get offended because he can't understand my thick banjo pickin' southern accent? No.
This could have been a teachable moment for Kellie, to learn that not every person on the other end of the phone is going to be who you expect it to be, and that some might not handle her with kid gloves if they don't know who she is. She may have special needs but she isn't stupid. Sheesh. I'm sure she could be taught to understand that the world isn't all beer and Skittles.
There's a lesson for the protective little sister in this, too: you can't put padding around everything in the world that may be harmful to people with special needs. You can't force the world to walk on eggshells so your special needs sister is never confronted with ugly reality.
Instead, this girl's sister is trying to drum up a witch hunt to get this hacky morning guy fired for basically doing his job and being 'edgy'. If anyone deserves scorn, it's her. If the transcript had shown him to be more insulting and callous I might side with the sister, but the DJ didn't mock her Down's Syndrome because he didn't know she had it! This is misdirected anger at its finest, IMHO, and the sister does not deserve the publicity for what is basically a minor incident at an irrelevant station in a small town. Hell, the transcript even shows Mo contemplating the repercussions of his act on air, meaning that he was at least partially aware that what he did might not go over well with the overly-sensitive listeners.
You can't expect a radio host to be 'edgy' then expect them to second-guess everything they do, otherwise it'll turn into any other lame John Tesh/unfunny wacky morning zoo type show. Either stand behind them when they step in it, or blow out the show and put in some generic inoffensive BS. Considering the format, generic bland crap is probably more appropriate, anyway.