Yeah that's true, even when the guest is well-equipped to debate they're going on a show watched by people with all opposing viewpoints. Case in point, McCain on The Daily Show the other day. Didn't matter what he said, he wasn't going to get so much as a head nod from the audience and Jon Stewart was going to be rolling in lulz and applause. I think a lot of times it's not intentional, just a side effect of being on a show that opposes every fiber in your body...
But the Daily Show isn't a real news program and isn't supposed to provide objective news, and is stated entertainment so it's ok and not really the straw man they're engaging it.
But when you have stations like FOX and CNN that are actually supposed to be objective and truly be fair and balanced doing the same thing, that is where the problem is.