But see, that's the problem! People keep jumping on her background as an excuse, but we see in her own recollections in Book 4 that she had the closest and most affectionate relationship with Tywin of the three children (though we see that the relative decency of each one seems inverse to his or her relationship with Tywin - Tyrion was practically a child-abuse victim and is the best by far, while Cersei who was treated better than Jaime makes him look honorable and virtuous), but Tyrion and Jaime have at least a cursory understanding of right and wrong. Jaime really seems to be somewhat spoiled by having never had to truly be tried or tested - his tragic background is in having everything come so easily to him that he is completely lacking in compassion or empathy and has never been trained to obey any sort of moral code other than his family's reputation or interests. With that as the only moral compass, much of his actions can be understood, if not justified, particularly in light of his drunken rant to Catelyn. Cersei however, is spoiled in the classical sense, having assumed a sense of entitlement from her upbringing and absorbed an ethos of ruthlessness, combining to strip her of any moral yardstick beyond her own wishes and whims. But instead people argue that her father mistreated her or something which justifies her own behavior, that being spoiled somehow excuses or justifies her. Diagnosis is not a cure. The word "spoiled" is used for a reason.

She didn't. Tyrion actually works out that it was Joffrey and only tells Jaime who seems to think it might be possible. Cersei had nothing to do with it and doesn't seem to know (or care) who was behind it. If any adult had anything to do with it, it was a careless drunken remark by Robert about putting Bran out of his misery. Joffrey swiped the dagger Robert had won betting on the tourney (betting against Jaime and rubbing it in his face), and armed a minion with it to kill Bran. He gives himself away when he hacks up Tyrion's book at his wedding breakfast and boasts "I am no stranger to Valyrian steel." Tyrion makes the connection at that point, and offers to replace the book with a dagger he describes like the one used against Bran. Joffrey's reaction to the description confirms it to Tyrion and following the meal he questions Sansa to ascertain Joffrey's motivation.

That's sort of what I got, but I was influenced by foreknowledge from the books. I felt it might have seemed to the viewers as if she was actually sympathetic. Combined with her later chat with Robert it might cause people to more readily accept her justifications, taking her claims of loving her children at face value. And I don't read her character from the books as dangerous, except in the sense of being in a position of great power with absolutely no compunctions about doing whatever she wishes at all. She's dangerous in the way that an impulsive six-year-old is behind the wheel of a tractor trailer truck. When you get the whole picture of what was going on in the first book, her seeming control of the situation is actually a combination of a pose and arrogant false assumptions of her own power and invulnerability. She herself later admits that Ned might still have won if not for a couple of lucky breaks, and in retrospect, given that Petyr has been manipulating this whole confrontation, you have to see his betrayal of Ned as the real deal-breaker, rather than any cunning of Cersei's.

Agreed. They did do that better and more noticeably in the series, whereas in the book it was earlier and more gradual and gave the impression instead that their relationship had simply been mended.