When you start sympathizing with the defendant!
Call me bonkers, but having spent all this time watching the trial day after day, poring over all the details of her case, reading her jailhouse letters, watching her in trial and noting every expression on her face, it's only natural that you should start "identifying" with the object of all this obsession. It's like when you've delved so deeply into the details of a person's life and psyche you can't help but start feeling 'attached.' Like you've come to know that person.
Unfortunately, Caylee should absolutely be the focus, but it is Casey who is on trial here, so she gets all of the attention. And by sympathizing I do not mean that I feel she is innocent - but I don't hate her with the same venom that some others here have expressed. I see it as an all round tragedy - not only in the case of Caylee's murder, but also in how KC had to go ruin her life like that when she had no reason to, when she had the rest of her life ahead of her.