I have a slightly different take on this. I think little kids find it slightly terrifying that they have the power to hurt their parents. They need to know that their parents are strong enough to still be calm and in control and emotionally okay, even if they (the kid) flails against them.
This struck me from the original post: "After his massive tantrum this morning he started crying and saying that he was afraid no one in the family would like him anymore because he is so mean." To me that sounds like a kid who is already freaking out about his power to hurt other people.
Excellent points, MegMeg. I have thought this about DS in the past; although he has never said "I hate you," we did have a stretch of unusually bad behavior. Because his birthmother abandoned him (at age 6, not as an infant - he was already living with his dad & me full-time and she just stopped calling), I chalked it up to him trying to find out just how bad he had to be before we abandon him, too (assuming he thought he was too bad to keep his mother).
We never explicitly discussed it, although I did once say "you can never do anything so bad that I will stop loving you, so please stop trying to find that point. It doesn't exist." I have no idea whether he understood or not; eventually he got back to his normal self.
I assumed it was because of our unusual situation, but given MegMeg's comments, maybe kids in more traditional situations experience the same need to test.
